Energy use and CO2 emissions in the Mexican cement industry are analyzed for the period 1982-94. Using the Laspeyres index method, we estimate the relative importance of fuel intensity, clinker activity, the cement/clinker ratio, and the use of waste tires as an alternative fuel in the changes of clinker fuel use. Changes in CO2 emissions are divided into energy intensity, cement activity, the cement/clinker ratio, and primary and final fuel-mix effects. The study shows that changes in all factors except for clinker activity drive fuel use down. Overall CO2 emissions are reduced by changes in real energy intensity and the clinker/cement ratio, while the primary fuel-mix effect (which accounts for changes in the share of final energy used to produce both cement and electricity) and cement activity drive emissions up.