Cogeneration, or Combined Heat and Power, is generally recognized as a set of technologies contributing to the more efficient use of fossil fuels. After the energy reform in Mexico, efficient cogeneration plants can generate and trade Clean Energy Certificates, to the extent a certain efficiency threshold is exceeded. According to official planning documents, a significant fraction of Mexico's targeted clean power production is expected to come from efficient cogeneration; this assumption is critically examined. The official methodology for determining clean power contributions from cogeneration is studied in detail, and the expected clean electricity fractions for several case studies are calculated. The efficiency figures determined in this step are then combined with an assessment of the potential for cogeneration in Mexico, the current installed cogeneration capacity, and the official growth figures, in order to estimate the expected clean power contribution from efficient cogeneration through 2030. Since the clean power fraction from cogeneration is determined through an accounting procedure it is potentially prone to data mishandling or even manipulation. It is concluded that significant possibilities for accounting failures exist and that efficient cogeneration plants generating Clean Energy Certificates should be equipped with a continuous monitoring system to ensure correct accounting.