Alireza Amirteimoori - Department of Mathematics, Islamic Azad University, Rasht-Iran
Sohrab Kordrostami - Department of Mathematics, Islamic Azad University, Lahidjan-Iran

This paper discusses the problem of multi-period data envelopment analysis (DEA). We consider the performance of a production unit in the course of T periods. The proposed DEA models not only measure the efficiency across all periods, but also they provide the efficiency measures for each of the periods. The applicability of the models developed is illustrated in the context of the analysis of gas companies performance

Data envelopment analysis, technical efficiency, overall efficiency