This study seeks to assess the macroeconomic performance of 54 (out of the 57) selected member countries of the Organization of the Islamic Cooperation (formerly known as Organization of the Islamic Conference), OIC for the period 2003- 2007, by utilizing the output-oriented DEA model under the assumption of variable returns to scale, VRS. The complexity of OIC as the second largest inter-governmental organization after the United Nations motivates us to undertake this study. The 57 member countries are dispersed over a large geographical region spanning over four continents. As a group, the OIC countries account for one-sixth (or 16.67%) of the world’s area, extending from Albania (Europe) in the North to Mozambique (Africa) in the South, and from Guyana (Latin America) in the West to Indonesia (Asia) in the East. OIC community also exhibits high level of income divergence with huge gap between the rich and the poor countries. Based on 2007 statistics, the average GDP per capita for OIC as a group is US$2595, ranging from a low US$206 (for Guinea-Bissau) to a high US$72849 (for Qatar) (SESRIC, 2008; Central Intelligence Agency, 2010). This reflects a difference of 354 times between the richest and the poorest. Thus a study of an organization with such high level of heterogeneity is likely to produce interesting (and probably contradicting) findings.