The objective of this study was to evaluate iso-butanol (C4H9OH) as an alternative fuel for spark ignition engines. Unlike methanol (CH3OH) and ethanol (C2H5OH), iso-butanol has not been extensively studied in the past as either a fuel blend candidate with gasoline or straight fuel. The performance of a single cylinder engine (ASTM=CFR) was studied using alcohol-gasoline blends under different input parameters. The engine operating conditions were: three carburetor settings (three different fuel flow rates), spark timings of 5°, 10°, 15°, 20°, and 25° BTDC, and a range of compression ratios from a minimum of 7.5 to a maximum of 15 in steps of one depending on knock. The fuels tested were alcohol-gasoline blends having 5%, 10%, 15%, and 20% of iso-butanol, ethanol, and methanol. And also as a baseline fuel, pure gasoline (93 ON) was used. The engine was run at a constant speed of 800 RPM. Torque, power, brake specific fuel consumption (BSFC), and thermal efficiency were determined at all the operating conditions. A direct comparison was drawn among the three alcohol blends and pure gasoline.Increasing alcohol content of the blend resulted in improving the anti-knock quality of the fuel but decreasing the power, and increasing BSFC. Thermal efficiency remained comparably constant within the range of fuel alcohol contents (5-20%). Methanol, ethanol, and iso-butanol showed nearly the same anti-knock effect. Iso-butanol blends resulted in more power, higher thermal efficiency, and lower BSFC than corresponding methanol and ethanol blends. Gasoline showed better results for torque, power, BSFC, and thermal efficiency than any of the blends studied.