Research on the Trade Characteristics of Conventional Energy Network Countries: Based on the Trade Characteristics of Leading Countries

Abstract

To study the trade characteristics and important trends of leading countries in conventional energy networks, this paper uses trade data on coal, oil and natural gas based on complex network theory; constructs a comprehensive directed weighted network; and analyzes the trade relations, trade volume, betweenness centrality and trade groups of China, the United States, Russia and Saudi Arabia. The results show that import and export trade relations exhibit the characteristics of power-law distribution, but the four countries are developing toward diversified trading partners. The United States has the greatest advantage in obtaining conventional energy and has the strongest control over energy. China’s advantage in obtaining conventional energy shows a downward trend, but its control over energy is second only to the United States. Saudi Arabia has the least advantage in obtaining energy and the weakest control, and it is an energy supplier. Russia’s trading bloc is the most stable. These four countries played a leading role in their trade bloc in most years.

1. Literature Review of Energy Trade and Complex Networks

Energy has always been among the important issues affecting national economic development and social progress, and energy is also an indispensable fuel for human survival and development. However, energy production and energy consumption are characterized by regional differences. Therefore, countries can obtain the energy needed for their economic development by participating in international trade. At the same time, the lack of energy will affect the normal development of a national economy; therefore, all countries should ensure the stable supply of their own energy. In international trade, countries should formulate their own trade strategies according to their own development. If we want to formulate a scientific trade strategy, we must accurately grasp the market pattern of energy trade.

1.1. Research on Energy Trade

Energy is the most common commodity in international trade, and it is also the main object of research by scholars. Scholars use different methods to summarize energy research. Beltramo et al. [1] constructed a trade model (GTM) for the natural gas market in North America. Research and analysis show that natural gas in North America is basically a self-sufficient system. Messner [2] constructed the natural gas trade model (GATE), and the results show that the GATE model plays an important role in studying the trade strategies used in future natural gas trade. Zwart and Mulder [3] analyzed the European natural gas market by constructing the NATGAS model, and the NATGAS model calculates the long-term impact of the policy on the price and production of natural gas. Holz et al. [4] constructed a European natural gas supply model (GASMOD) and analyzed exports to Europe and the supply of natural gas within Europe.

These studies are of great significance to the study of international energy trade. However, international energy trade is a complex system involving many countries. We can use complex network methods to better analyze the connection between the whole and the individual and perform a quantitative analysis of this system.

1.2. Research on Energy Trade Based on Complex Networks

Complex networks have become an emerging research hotspot in recent years, and in essence they regard the connection between individuals as an actual network to better analyze the relationship between individuals in the network. The use of complex network methods for energy research can be summarized as follows: An et al. [5] constructed a complex network model based on oil trade, analyzed the relationship between countries with the same trading partners and found that there is a correlation between the same trading partner countries. Zhong et al. [6] used oil trade data to construct weighted and unauthorized trade networks, analyzed the evolution of the trade community in the network and found that there were different characteristics between the two networks. Chen Weidong et al. [7] constructed a complex network model of oil price fluctuation and considered that the degree and cumulative distribution of nodes in the network have a power law. Gao Xiangyun et al. [8] used the coarse-grained method to convert spot and futures prices of oil into a group of letters representing price fluctuations and constructed a complex network model for the linkage between futures and spots. Wang Zhaojun et al. [9] constructed a complex network using the data of China–US crude oil import sources. It is believed that when different trading countries avoid risks, they should choose a partner that suits them according to their own objective environment to better implement the diversification strategy. Ji et al. [10] constructed the global oil trade network and found that it can be divided into three trade groups. Zhang et al. [11] used complex network link prediction methods and used lithium carbonate, an important raw material for lithium-ion batteries, as the research object to predict the potential trade relations between countries with low levels of lithium carbonate abundance.

As people have developed a deeper understanding of the real world, probably at the end of the 20th century, a new era in the study of complex networks was truly opened. First, Watts et al. [12] proposed the small-world network model, which not only has the characteristics of a high aggregation coefficient of regular networks but also the characteristics of a small average path length of random networks. Second, Barabasi et al. [13] proposed a scale-free network model that has the characteristics of growth and selection and explains the scale-free phenomenon in the real world from these two aspects. It is believed that most complex network systems in the real world are dynamic, open and free. It is the small-world model and scale-free network model that promote the development of complex networks. Since then, complex networks have been widely used in management [14], physics [15], chemistry [16], biology [17], technology [18], and international trade [19,20] research in other fields.

Based on the above literature, it was found that the research methods and models used by scholars are different, and the selected research objects are also different. The use of the complex network method in international trade can more clearly reflect the characteristics of the whole network and the relationship between individuals, provide a new method and perspective for the study of international trade, and provide a theoretical basis for this study. However, most scholars choose a single object for energy research and study the whole trade network. Therefore, this paper adds coal, oil and natural gas together to construct a conventional energy trade network and selects the main countries in the trade network to analyze the trend of their trade characteristics and importance to provide some suggestions for the countries to formulate a scientific and reasonable trade strategy and ensure national economic development.

2. Data and Method

2.1. Construction of an International Energy Network

This study uses the energy trade data for coal (Code: 270119), oil (Code: 270900) and natural gas (Code: 271111) from 2010 to 2019, all of which are from UN COMTRADE. Through data preprocessing, the three energy sources are converted into standard coal and added together. First, the trade volume of the three energy sources is converted into standard coal according to their respective standard coal coefficients. Then, we add up the countries that have two or three types of trade in the direction of imports or exports, and only one kind of trade between countries remains unchanged. We use the aggregated standard coal trade volume as the weight of the conventional energy network, constructing a conventional energy trade network. In a directed weighted network, if the energy trade volume exported from the ith country to the jth country is w, then a weighted arrow with country i pointing to country j is established in the network. The network is expressed in the form of an adjacency matrix as formula (1):

$$F\left(t\right)=\left[\begin{array}{ccc}{w}_{1,1}\left(t\right)& \cdots & w_{1,j}\left(t\right)\\ ⋮& \ddots & ⋮\\ w_{i,1}\left(t\right)& \cdots & w_{i,j}\left(t\right)\end{array}\right]$$

(1)

In the formula, w_i,j(t) is the trade volume of standard coal exported from country i to country j in year t.

2.2. In-Degree and Out-Degree of Nodes

In the international trade network, the in-degree of a node represents the number of import trading partners owned by the node country, and the out-degree of a node represents the number of export trading partners owned by the node country.

The in-degree of node i is defined as:

$$k_i^{in}={\displaystyle \sum _{j=1}^N{a}_{ji}}$$

(2)

The out-degree of node i is defined as:

$$k_i^{out}={\displaystyle \sum _{j=1}^N{a}_{ij}}$$

(3)

In the formula, the symbol N is the number of countries participating in national trade, a_ji is whether the node j country exports to the node i country, if yes, it is recorded as 1, otherwise it is 0. a_ij is whether the node i country exports to the node j country, if yes, it is recorded as 1, otherwise it is 0.

2.3. Weighted In-Degree and Weighted Out-Degree of Nodes

In the directed weighted network of energy international trade, the weighted degree includes the weighted in-degree and weighted out-degree. The weighted in-degree of node i is defined as:

$$s_i^{in}={\displaystyle \sum _j^n{w}_{ji}}$$

(4)

The weighted out-degree of node i is defined as:

$$s_i^{out}={\displaystyle \sum _j^n{w}_{ij}}$$

(5)

In the formula, the symbol j is the national node, the symbol n is the total number of node countries in the network, and the symbol W_ij represents the weight of the edge from node i to node j.

2.4. Node Betweenness Centrality

The betweenness centrality of a node refers to the proportion of the shortest path through the node in the network. The greater the betweenness centrality, the greater the country’s role in the conduction of energy in the network. That is, the transfer ability is strong, and the control ability is relatively strong. The betweenness centrality of node i is defined as:

$$G_B\left(i\right)={\displaystyle \sum _{j,k}\frac{g_i\left(j,k\right)}{g\left(j,k\right)}}$$

(6)

In the formula, the symbol g(j,k) is the total number of shortest paths between node j and node k; the symbol g_i(j,k) represents the number of shortest paths between node j and node k passing through node i; G_B(i) represents the transfer ability of node i in the whole network.

3. The Role and Status of Major Countries in Conventional Energy

3.1. The Basic Situation of Imports and Exports of the Four Major Countries

Through the analysis of the import and export energy trade volume of various countries participating in conventional energy trade from 2010 to 2019, China and the United States are countries with large and relatively stable energy imports. Russia and Saudi Arabia are countries with large and relatively stable energy exports. Therefore, we selected these four countries and studied their role and status in the international trade of conventional energy.

We calculated the trade volume of conventional energy imported by China and the United States and processed them in descending order to obtain their ranking of imported energy, as shown in

Table 1. Ranking of conventional energy imports between China and the United States.

Country	2010	2011	2012	2013	2014	2015	2016	2017	2018	2019
China	4	4	3	3	3	2	2	2	2	6
The United States	1	1	2	1	4	4	3	3	3	3

. The US trade volume of imported conventional energy was relatively stable, and the import volume was relatively large. It became the largest importer of conventional energy in 2010, 2011 and 2013. Before 2019, China’s trade volume of imported conventional energy increased year by year but dropped sharply in 2019, which was affected by the US trade war.

We calculated the trade volume of conventional energy exported by Saudi Arabia and Russia and processed them in descending order to obtain their ranking of exported energy, as shown in

Table 2. Ranking of Saudi Arabia and Russia in exporting conventional energy.

Country	2010	2011	2012	2013	2014	2015	2016	2017	2018	2019
Saudi Arabia	1	1	1	1	2	2	2	2	2	3
Russia	2	2	2	2	3	3	4	3	4	2

. The trade volume of Saudi Arabia’s export of conventional energy was relatively stable and large, becoming the largest exporter in 2010–2013. Russia’s export ranking was basically second or third, and it was also a relatively stable exporter.

The import and export values of standard coal of the United States, China, Russia and Saudi Arabia are shown in Figure 1. Figure 2 shows the proportion of coal, oil and natural gas imports and exports of the United States, China, Russia and Saudi Arabia. The figure shows that the import of standard coal for conventional energy in the United States shows a downward trend. In 2014, the import of standard coal fell to the lowest point because a large amount of shale oil was mined in North Dakota, Texas and New Mexico in 2014, resulting in a decline in imported standard coal. Standard coal imported from the United States was mainly concentrated in oil fuels. In 2014, a large amount of shale oil exploitation in North Dakota, Texas, New Mexico and other regions of the United States allowed the United States to achieve leapfrog growth in its position of exporting natural gas, and the export of natural gas reached the highest point in 2015. The trade volume of imported coal in the United States was relatively small, and it showed a downward trend year by year from 2010 to 2019. Although the amount of imported coal was relatively small, it was also accompanied by coal export, which showed an upward trend year by year. Compared with the United States, China’s standard coal imports showed an upward trend, reaching the highest point in 2016, and China’s standard coal import exceeded that of the United States in 2014–2018. In 2019, however, the import of standard coal fell sharply, which was caused by the US trade war against China. China’s exports of standard coal were very small, and China’s standard coal imports and exports were mainly concentrated in oil fuels. Russia’s export volume of conventional energy standard coal fluctuated slightly from 2010 to 2019, reaching a maximum in 2017. The main export standard coal was concentrated in oil. Saudi Arabia’s conventional energy exports showed a downward trend from 2010 to 2019. In 2019, the export volume of standard coal lagged behind Russia, and the export volume reached the lowest point. Unlike Saudi Arabia, Russia exported a small amount of natural gas in addition to coal and oil. Russia mainly imported coal and a small amount of oil, and Saudi Arabia mainly imported coal.

3.2. Analysis of the Import and Export Trading Partners and Trade Volume of Four Major Countries

In Figure 3, we summarize the top 20 import or export volumes for four countries. The horizontal axis represents the number of trade relations and the vertical axis represents the volume of trade. For the volume of import trade, we analyzed China and the United States. For export trade volume, we analyzed Russia and Saudi Arabia. The figure shows that the standard coal trade relations of these four major countries have one thing in common, that is, the number of relationships with high-standard coal trade accounts for very few of the total number of relationships. Most relationships only occupy a small amount of standard coal trade. The phenomenon shown by the United States and Saudi Arabia is more obvious. Relatively speaking, the phenomenon shown by China and Russia is not very obvious. The reason for this phenomenon may be that the United States and Saudi Arabia tend to trade on a large scale with a small number of fixed countries. However, in some years, this phenomenon may be more obvious due to the influence of certain external factors, such as the standard coal import relationship shown by China in 2016. This shows that the United States and Saudi Arabia’s trade in standard coal was more concentrated on a small number of trading partners. China and Russia are becoming more diversified in standard coal trade.

The top 10 trading partners of each of the four major countries are summarized and the results are presented in

Table 3. Top 10 import trading partners of the United States.

Year	Ranking
	1	2	3	4	5	6	7	8	9	10
2010	Canada	Venezuela	Saudi Arabia	Mexico	Nigeria	Iraq	Columbia	Angola	Russia	Algeria
2011	Canada	Saudi Arabia	Venezuela	Mexico	Nigeria	Angola	Iraq	Columbia	Russia	Algeria
2012	Canada	Saudi Arabia	Venezuela	Mexico	Iraq	Nigeria	Columbia	Kuwait	Ecuador	Angola
2013	Canada	Saudi Arabia	Venezuela	Mexico	Columbia	Iraq	Kuwait	Nigeria	Ecuador	Angola
2014	Canada	Saudi Arabia	Venezuela	Mexico	Iraq	Kuwait	Columbia	Ecuador	Brazil	Angola
2015	Canada	Saudi Arabia	Venezuela	Mexico	Columbia	Ecuador	Iraq	Kuwait	Brazil	Angola
2016	Canada	Saudi Arabia	Venezuela	Mexico	Columbia	Iraq	Ecuador	Kuwait	Nigeria	Angola
2017	Canada	Saudi Arabia	Venezuela	Mexico	Iraq	Columbia	Nigeria	Ecuador	Brazil	Kuwait
2018	Canada	Saudi Arabia	Venezuela	Mexico	Iraq	Columbia	Nigeria	Ecuador	Brazil	Russia
2019	Canada	Mexico	Saudi Arabia	Iraq	Columbia	Ecuador	Nigeria	Brazil	Russia	Trinidad and Tobago

,

Table 4. China’s top 10 import trading partners.

Year	Ranking
	1	2	3	4	5	6	7	8	9	10
2010	Saudi Arabia	Angola	Iran	Indonesia	Former Sudan	Russia	Oman	Venezuela	Iraq	Kazakhstan
2011	Saudi Arabia	Angola	Russia	Iran	Indonesia	Former Sudan	Oman	Venezuela	Iraq	Kazakhstan
2012	Saudi Arabia	Angola	Russia	Indonesia	Venezuela	Iran	Oman	Iraq	The United Arab Emirates	Kazakhstan
2013	Saudi Arabia	Angola	Russia	Indonesia	Oman	Iraq	Venezuela	Iran	The United Arab Emirates	Kazakhstan
2014	Saudi Arabia	Russia	Angola	Oman	Iraq	Iran	Venezuela	The United Arab Emirates	Indonesia	Qatar
2015	Saudi Arabia	Russia	Angola	Oman	Iraq	Iran	Venezuela	The United Arab Emirates	Indonesia	Kuwait
2016	Myanmar	Saudi Arabia	Russia	Angola	Iraq	Oman	Iran	Venezuela	Brazil	Indonesia
2017	Russia	Saudi Arabia	Angola	Iraq	Venezuela	Oman	Iran	Brazil	Australia	The United States
2018	Saudi Arabia	Russia	Angola	Iraq	Oman	Brazil	Australia	Iran	Venezuela	Indonesia
2019	Russia	Brazil	Qatar	Britain	Indonesia	The United States	Columbia	Malaysia	Congo	the Philippines

,

Table 5. Saudi Arabia’s top 10 export trading partners.

Year	Ranking
	1	2	3	4	5	6	7	8	9	10
2010	North America	Japan	The United States	China	South Korea	India	Singapore	Thailand	Spain	Italy
2011	North America	The United States	Japan	China	South Korea	India	Singapore	Bahrain	Italy	Spain
2012	North America	The United States	Japan	China	South Korea	India	Singapore	Italy	South Africa	France
2013	North America	The United States	Japan	China	South Korea	India	Bahrain	South Africa	France	Singapore
2014	North America	Japan	The United States	China	South Korea	India	France	Bahrain	Singapore	South Africa
2015	North America	The United States	China	South Korea	India	France	Bahrain	Singapore	Spain	Italy
2016	The United States	Japan	North America	China	South Korea	India	Singapore	Bahrain	France	South Africa
2017	Japan	The United States	China	South Korea	India	Bahrain	Singapore	South Africa	France	Spain
2018	Japan	China	The United States	South Korea	India	Bahrain	Singapore	South Africa	France	Spain
2019	Japan	India	South Korea	The United States	Thailand	France	South Africa	Singapore	Indonesia	Italy

and

Table 6. Russia’s top 10 export trading partners.

Year	Ranking
	1	2	3	4	5	6	7	8	9	10
2010	Netherlands	Germany	Italy	Poland	The United States	Japan	China	South Korea	Belarus	France
2011	Netherlands	Germany	Poland	Italy	China	Belarus	Japan	South Korea	The United States	Finland
2012	Netherlands	Germany	China	Poland	Belarus	Italy	Japan	South Korea	Sweden	Lithuania
2013	Netherlands	Germany	China	Poland	Belarus	Italy	Japan	South Korea	Finland	Lithuania
2014	Netherlands	China	Germany	Belarus	Poland	Italy	Japan	South Korea	Finland	Sweden
2015	Netherlands	China	Germany	Belarus	Poland	Japan	Italy	South Korea	Finland	Sweden
2016	Netherlands	China	Germany	Poland	Japan	Italy	South Korea	Belarus	Lithuania	Sweden
2017	China	Netherlands	Germany	Poland	Belarus	Japan	Italy	South Korea	Finland	France
2018	China	Netherlands	Germany	Poland	South Korea	Japan	Italy	Belarus	France	Finland
2019	China	Netherlands	Germany	Belarus	South Korea	Poland	Japan	Italy	Svalbard and Jan Mayen, Norway	Finland

. As shown in Table 3, Canada’s trade volume of conventional energy exports to the United States has always ranked first, which shows that Canada was the largest trading partner of the United States in the trade volume of conventional energy imports from 2010 to 2019. Saudi Arabia, Venezuela and Mexico are also major trading partners of the United States for importing conventional energy. Other important import trading partners include Iraq, Nigeria, Colombia, and Ecuador. In 2010 and 2011, Algeria ranked 10th among the import trading partners of the United States, but it never entered the top 10 US import partners in 2012–2019. As a major exporter, only in 2010, 2011, 2018 and 2019 did it rank among the top 10 import partners in the United States, and the ranking was relatively low. The United States only appeared in the top 10 of Russia’s export trading partners in 2010 and 2011.

The distribution of the source countries of China’s imported conventional energy tended to be more diversified. Table 4 shows that China’s main sources of imported conventional energy were Saudi Arabia, Russia, and Angola; among them, Saudi Arabia basically ranks in the top three among China’s imported conventional energy partners. It was in first place from 2010 to 2015, but in 2019, Saudi Arabia fell out of the top 10 among China’s conventional energy import partners. Russia’s ranking among China’s import trading partners is basically in the top three, and Russia’s ranking has shown an upward trend over time. In addition, it ranked first in 2017 and 2019. This was caused by the deepening of the cooperation between China and Russia in energy, the vigorous construction of the Sino-Russian oil pipeline, and the use of renminbi in transactions. Indonesia, Oman, and Iraq are also important sources of imported conventional energy for China.

Table 5 shows that Saudi Arabia’s main export targets are North America, the United States, and Japan. Among them, North America ranked first in 2010–2015 and fell out of the top ten in 2017–2019. Japan’s ranking was basically in the top three and showed an upward trend. In 2015, Saudi Arabia did not export conventional energy to Japan, and Japan surpassed North America to rank first in the three years of 2017–2019. The United States ranked in the top three in most years and only ranked fourth in 2019. China, South Korea, India and Singapore are also major exporter targets of Saudi Arabia. Among them, China ranked in the top four in most years, and its ranking increased year by year. It only fell out of the top ten in 2019, which is directly related to the trade war launched by the United States against China. In general, Saudi Arabia’s export targets are relatively stable. The top 10 trading partners of the decade include only 14 countries. India, Singapore, the United States and South Korea appeared in every year, and China and Japan appeared nine times in 10 years.

Table 6 shows that Russia’s main export targets are the Netherlands, China, and Germany. These three countries are basically in the top three rankings. Among them, the Netherlands was ranked first from 2010 to 2016. The ranking dropped by one place from 2017 to 2019 and ranked second. The Netherlands was Russia’s main export target and was relatively stable throughout the observation period from 2010 to 2019. Overall, China’s ranking has shown a gradual upward trend over time, until it ranked first in 2017. This was caused by the deepening of the cooperation between China and Russia in energy, the vigorous construction of the Sino-Russian oil pipeline, and the use of renminbi (RMB) in transactions. Germany dropped from first place to second place before 2013, and it is also the main and stable export target. Other major export targets are Poland, Belarus, Italy and other countries.

3.3. Analysis of Betweenness Centrality in the Four Main Countries

3.3.1. Centrality of the Four Major Countries

Centrality reflects the central position of a country, which is the total distance of a country from other countries. If a country’s location is closer to the center, then the country will be able to obtain resources more easily and faster. The centrality of the United States, China, Russia and Saudi Arabia is shown in Figure 4. The figure shows that the United States had the highest centrality, except for the three years of 2014, 2015, and 2019, and the central position of the United States has shown an upward trend. The China–US trade war in 2019 will have a certain impact on the central position of the United States. The central position of China has shown a downward trend as a whole and showed an upward trend from 2010 to 2014. In 2011, 2012, and 2014, it surpassed Russia to become the second largest country in the central position. Since 2014, it has shown a downward trend, and the central position has dropped by one place. The central position of Russia has shown an upward trend as a whole. Since 2015, Russia has become the second centrally located country. Saudi Arabia is the country with the lowest central location, reaching its highest peak in 2015.

3.3.2. Betweenness in the Four Main Countries

Betweenness reflects the intermediary capacity of a country, and betweenness ability is the ability of a country to control the circulation of resources in the network. The betweenness of the United States, China, Russia and Saudi Arabia is shown in Figure 5. The figure shows that the United States has the highest betweenness, followed by China. During the entire observation period, the betweenness fluctuated sharply, reaching its lowest point in 2015, which has a clear relationship with the decline in crude oil prices in 2015. In 2019, China’s betweenness declined more, which has a clear relationship with the trade war launched by the United States against China, and the United States was less affected. Russia ranked third in most years and had a slight upward trend. Saudi Arabia had the least betweenness. It was relatively stable from 2010 to 2015, rose to its peak in 2016, and then showed a downward trend year by year.

3.4. Analysis of Trade Groups in the Four Main Countries

The trade group in a complex network corresponds to a subset of nodes in the network. Such a subset will also be formed between countries in an international trade network. The relations between countries in the same trade group are relatively close, while the relations between countries in different groups are relatively loose. This article uses the modularization index in Gephi software to calculate the trade groups formed each year and analyzes the trade groups as follows. Figure 6 shows the distribution of trade groups in 2019.

3.4.1. Trade Group Size

Trade group size is the number of trading countries included in the group. Figure 7 shows the changes in the group size of the trade groups where the United States, China, Russia, and Saudi Arabia are located. The figure shows that the trade scale of the other three countries except Russia fluctuates sharply and shows the trade group where Russia is the largest in most years. The trade group in which the United States is located has the largest scale in individual years and is in the middle position in most years. The trade group in which China is located was relatively small before 2013 but became the largest trading group in 2014 and 2015. The trade group in which Saudi Arabia is located is the smallest in most years.

3.4.2. Stability of Trade Groups

Autoregressive equation Y(t) is used to calculate the stability of trade groups in four countries, that is, how much overlap there is between the two groups from year t_m to year t_m+1 in a group. The greater the value of the autoregressive equation Y(t), the higher is the stability of the trade group, and conversely, the lower the value, the worse is the stability of the trade group. The autoregressive equation Y(t) is defined as:

$$Y_t=\frac{\left|Y\left(t_m\right)\cap Y\left(t_{m+1}\right)\right|}{\left|Y\left(t_m\right)\cup Y\left(t_{m+1}\right)\right|}$$

(7)

In the formula, the symbol Y(t_m) refers to the trade group in t_m year, $\left|Y\left(t_m\right)\cap Y\left(t_{m+1}\right)\right|$ refers to the cardinality of the intersection between the trade group in year t_m and the trade group in year t_m+1 in the next year, that is, the number of public members between the two groups. $\left|Y\left(t_m\right)\cup Y\left(t_{m+1}\right)\right|$ refers to the cardinality of the union between the trade group in year t_m and the trade group in year t_m+1 in the next year, that is, the total number of members of the two groups minus the number of public members.

The stability of trade groups in which the four major countries are located is shown in Figure 8. The figure shows that the stability of Russia’s trade group is relatively high and relatively stable, but the stability shows a downward trend. The stability of the trade groups in which the United States and Saudi Arabia are located is also relatively high, but the fluctuations are relatively large. The stability of the trade group in which China is located is the lowest, but the volatility is relatively stable, and the stability of the group during the period of 2014–2015 was higher than that of the United States.

Changes in group stability reflect changes in member states within the group.

Table 7. The four main countries are in the trade group. (a) Trade groups in which the four major countries are located in 2010; (b) trade groups in which the four major countries are located in 2011; (c) trade groups in which the four major countries are located in 2012; (d) trade groups in which the four major countries are located in 2013; (e) trade groups in which the four major countries are located in 2014; (f) trade groups in which the four major countries are located in 2015; (g) trade groups in which the four major countries are located in 2016; (h) trade groups in which the four major countries are located in 2017; (i) trade groups in which the four major countries are located in 2018; (j) trade groups in which the four major countries are located in 2019.

(a)
Rank	Group 1	Group 2	Group 3	Group 4	Group 5	Group 6	Group 7	Group 8
1	Russia	China	The United States	Saudi Arabia	Japan	Iraq	Botswana	Fiji
2	Netherlands	Angola	Venezuela	Iran	South Korea	Kuwait	Zimbabwe	Tonga
3	Britain	Former Sudan	Canada	South Africa	The United Arab Emirates	Israel
4	Italy	Yemen	Nigeria	Mozambique	Qatar	Bahrain
5	Germany	North Korea	Spain	India	Indonesia	Zambia
6	Svalbard and Jan Mayen, Norway	Mauritania	Mexico	Pakistan	Australia	Palestine
(b)
Rank	Group 1	Group 2	Group 3	Group 4	Group 5	Group 6	Group 7
1	China	The United States	Russia	Saudi Arabia	Japan	Iraq	Zimbabwe
2	Indonesia	Venezuela	Canada	Iran	India	Israel	Botswana
3	Nigeria	Mexico	Netherlands	North America	South Korea	Palestine
4	Angola	Latin American Integration Association	Britain	South Africa	Qatar
5	Spain	Columbia	Italy	Greece	The United Arab Emirates
6	Brazil	Trinidad and Tobago	Svalbard and Jan Mayen, Norway	Bahrain	Australia
(c)
Rank	Group 1	Group 2	Group 3	Group 4	Group 5	Group 6	Group 7	Group 8
1	China	The United States	Russia	Saudi Arabia	Iraq	Micronesia	Fiji	Iraq
2	India	Venezuela	Netherlands	The United Arab Emirates	Israel	Guam	Tuvalu	Israel
3	Indonesia	Canada	Britain	Japan	Sri Lanka	Palau	Kiribati	Sri Lanka
4	Kuwait	Nigeria	Germany	South Korea	Bahrain	Marshall Islands	Samoa	Bahrain
5	Angola	Spain	Italy	North America
6	Iran	Mexico	Kazakhstan	Qatar
(d)
Rank	Group 1	Group 2	Group 3	Group 4	Group 5	Group 6	Group 7
1	Saudi Arabia	China	Russia	The United Arab Emirates	South Africa	Fiji	Nicaragua
2	The United States	Angola	Netherlands	Japan	Mozambique	Tuvalu	Curacao
3	India	Oman	Britain	South Korea	Mauritius	Tonga	Salvador
4	Venezuela	Iran	Germany	Kuwait	Swaziland
5	Canada	Congo	Italy	Qatar	Ethiopia
6	Indonesia	South Sudan	Nigeria	Australia	Luxembourg
(e)
Rank	Group 1		Group 2		Group 3		Group 4
1	The United States		Saudi Arabia		Russia		Japan
2	Mexico		North America		Netherlands		The United Arab Emirates
3	China		the Philippines		Britain		South Korea
4	India		Pakistan		Germany		Iraq
5	Indonesia		Morocco		Italy		Qatar
6	Canada		Jordan		Kazakhstan		Kuwait
(f)
Rank	Group 1	Group 2	Group 3	Group 4	Group 5		Group 6
1	The United States	China	Saudi Arabia	Russia	The United Arab Emirates		Thailand
2	Mexico	India	North America	Netherlands	South Korea		Myanmar
3	Canada	Iraq	the Philippines	Britain	Japan
4	Venezuela	Indonesia	Bahrain	Germany	Qatar
5	Columbia	Nigeria	Pakistan	Italy	Kuwait
6	Ecuador	Angola	Latin American Integration Association	Kazakhstan	Australia
(g)
Rank	Group 1	Group 2	Group 3	Group 4	Group 5		Group 6
1	The United States	China	Saudi Arabia	Russia	India		South Africa
2	Mexico	Myanmar	North America	Netherlands	Japan		Mozambique
3	Canada	Thailand	Jordan	Britain	Iraq		Malawi
4	Venezuela	Angola	Latin American Integration Association	Italy	South Korea		Morocco
5	Columbia	Brazil	Oceania	Germany	The United Arab Emirates		Swaziland
6	Ecuador	Oman	Guinea	Spain	Kuwait		Zimbabwe
(h)
Rank	Group 1	Group 2	Group 3	Group 4	Group 5	Group 6	Group 7	Group 8
1	China	The United States	India	The United Arab Emirates	Britain	South Africa	Kuwait	Barbados
2	Russia	Mexico	Iraq	Japan	Israel	Mozambique	Oman	Belize
3	Netherlands	Saudi Arabia	Iran	Qatar	Switzerland	Mauritius	Zambia
4	Germany	South Korea	Nigeria	Australia	Ireland	Nepal
5	Svalbard and Jan Mayen, Norway	Canada	Italy	Malaysia	State of Palestine	Ethiopia
6	Angola	Indonesia	Kazakhstan	Singapore	Iceland	Kenya
(i)
Rank	Group 1	Group 2	Group 3		Group 4		Group 5
1	China	The United States	Russia		India		Mexico
2	Saudi Arabia	Canada	Netherlands		Iraq		The United Arab Emirates
3	South Korea	Venezuela	Britain		Nigeria		Oman
4	Japan	Columbia	Italy		Spain		Pakistan
5	Indonesia	Ecuador	Kazakhstan		Iran		New Zealand
6	Qatar	Chile	Germany		South Africa		Afghanistan
(j)
Rank	Group 1	Group 2	Group 3	Group 4	Group 5		Group 6
1	Russia	The United States	South Korea	India	Israel		Rwanda
2	China	Mexico	Saudi Arabia	Iraq	Bunker		Tanzania
3	Netherlands	Canada	Japan	Nigeria	Kenya
4	Britain	Indonesia	The United Arab Emirates	South Africa
5	Italy	Spain	Qatar	Venezuela
6	Germany	Columbia	Australia	Egypt

shows the various trade groups in the network from 2010 to 2019. The table displays the top 6 countries in terms of import and export trade volume of each member country in the group. The country represented by each column of the table is in the same trade group. The table shows that there were 8 trade groups in 2010, 2012 and 2017, which was the year with the largest number of trade groups in a decade. From 2010 to 2012, 2015 and 2016, the four major countries, the United States, China, Russia and Saudi Arabia, were in different trading groups and were the dominant countries of the trade group. Except for 2013, the United States was always the dominant country in the trade group in other years. Russia and Saudi Arabia have never appeared in the same trade group. Russia and China were in the same group twice, and Saudi Arabia and the United States were in the same group twice. China was the dominant country in the trade group from 2010 to 2013. China was in the same group as the United States, Russia, and Saudi Arabia in 2014 and from 2017 to 2019, and the size of the trade group is larger than China’s own in the group.

4. Conclusions

This article mainly studies the trade relations, trade volume, betweenness centrality and trade groups of the United States, China, Russia, and Saudi Arabia. Based on these results, we analyzed the trade characteristics and importance trends of the four main countries in the conventional energy trade network with the following conclusions:

(1)

China’s conventional energy imports show an upward trend, mainly importing oil; energy exports are minimal. The United States’ imports of conventional energy show a downward trend, with oil mainly being imported. In 2014, the massive exploitation of shale oil in the United States caused exported natural gas to grow by leaps and bounds. Russia’s conventional energy exports fluctuate slightly, and it mainly exports oil; energy imports are mainly concentrated in coal, with a small amount of oil. Saudi Arabia’s conventional energy exports show a downward trend, mainly importing and exporting coal and exporting oil.

(2)

The trade relations of the import trading partners of China and the United States show power-law distribution characteristics, and the trade relations of the export trading partners of Russia and Saudi Arabia show power-law distribution characteristics. The phenomenon shown by the United States and Saudi Arabia is more obvious. Relatively speaking, the phenomenon shown by China and Russia is not very obvious. However, the four countries are pursuing the diversification of trading partners to ensure trade security.

(3)

The largest import trading partner of the United States is Canada, and other major import partners are Saudi Arabia, Venezuela and Mexico. The distribution of China’s import trading partners tends to be diversified. The main import partners are Saudi Arabia, Russia, and Angola, and over time, trade relations with Russia have become increasingly closer. The main export targets of Saudi Arabia are North America, the United States, and Japan, and the export targets are relatively stable. Russia’s main export targets are the Netherlands, China, and Germany, among which the volume of energy exports to China is increasing.

(4)

The central position of the United States fluctuates sharply, but it is still in the most central position in the conventional energy trade network, which means that the United States has a relatively large advantage in obtaining conventional energy. Russia’s advantage in obtaining conventional energy is gradually increasing. Before 2014, China’s advantage in obtaining conventional energy gradually increased, but after 2014, the advantage gradually weakened. China should establish closer trade relations with other countries and increase its advantages in obtaining conventional energy. Saudi Arabia’s advantage in obtaining energy is relatively weak.

(5)

The United States has the strongest ability to control conventional energy and is an important hub country, but before 2015, the control ability showed a downward trend. The fastest decline in 2014 may be due to the large amount of shale gas produced in the United States in 2014, which increased its own energy reserves and reduced conventional energy imports. China’s ability to control conventional energy is very unstable. Saudi Arabia has the weakest ability to control conventional energy, which may be due to its relatively abundant conventional energy and the relatively small volume of imported conventional energy trade.

(6)

Russia’s trade group has the highest stability, but its stability weakened over time. The stability of China’s trade group is the weakest. China, the United States, Russia, and Saudi Arabia play a leading role in trade groups.