**1. Introduction**

Environmental issues are becoming more important as a consequence of growing pollution-generating technologies. Greenhouse gas emissions reduction is one of the main concerns of all societies in this century. A five percent reduction of greenhouse gas emissions on average was decided in the Kyoto Protocol for 2008–2012 compared with 1990. This reduction level was decided to be 50 percent on average in Copenhagen. Industries are one of the main sources of emissions production in all countries. The reduction path has been decided to be gradual, since cutting down the emissions may be possible because it they are a byproduct in industries. The key factor in emissions reduction is the performance and the efficiency of production technology. Data envelopment analysis (DEA) is a mathematical programming-based approach for efficiency analysis of a group of decision-making units (DMUs) proposed by [1]. In this paper, we propose new models for estimating the classical and environmental performance of multi-plant firms. Then we develop some new indices for capturing the environmental performance vs. classical economic performance at the local and global level. The proposed approach is utilized for the economic and environmental performance assessment of 46 power plants in Iran. The primary result emphasizes considering not only local environmental performance but also global performance to have a broad insight into environmental performance assessments. Primary results show that we have only a few power plants that are resistant to environmental performance at the country level when we use models with non-uniform scaling factors for desirable and undesirable outputs. This is due to the higher discrimination power of associated economic and environmental efficiency measures of these indices. Another important result is that the geographical location does not affect the environmental or economic performance. This finding encourages considering both local and global environmental performances to have a broad environmental performance that may be used for any type of local and global environmental planning by decision-makers. The rest of the paper is organized as follows. Section 2 reviews the relative literature with the classical and environmental efficiency analysis of multi plants firms. Section 3 provides the primary models and material in the first subsection. In the second subsection, we develop environmental multi-plant DEA models dealing with undesirable outputs. The third subsection proposes a mixed, uniform, and non-uniform multi-plant DEA model for considering desirable and undesirable outputs simultaneously. Section 4 applies the proposed models for local and global classical and environmental efficiency analysis of Iranian power plants.
