This work was undertaken to evaluate butanol as an alternative fuel for internal combustion engines- The evaluation was made by measuring the performance of a four-cylinder automotive spark-ignition engine when fueled with four different Fuels: (a) 100% unleaded-regular fuel was used for reference. (b) the test fuel, iso-butanol, was blended in amounts of 5, 10, 15, and 20% by volume with gasoline for the subject evaluation. (c) for comparison purposes, a 10% methanol-gasoline blend was used. (d) also for comparison, a 10% ethanol-gasoline blend was used. It was found that there was only about 2.5% reduction in the thermal efficiency of the test engine when 20% of the gasoline was replaced by butanol (the brake-specific-fuel-consumption, BSFC, increased by about 6.5%). Butanol was shown to be superior to both methanol and ethanol in terms of higher thermal efficiency (and correspondingly lower BSFC).