To measure the effect of CR on the engine’s performance, combustion and exhaust emissions in the SI engine, which was fueled with unleaded gasoline, pure ethanol and methanol, experimental work was done and the results of the investigation were compared to those values of unleaded gasoline. The results obtained from the tests at different CR levels of 8.0:1, 8.5:1, 9.0:1 and 9.5:1, at a constant engine speed of 2400 rpm, wide open throttle, and a stoichiometric mixture of the three different fuels can be summarized as follows: