Experimental tests were carried out on a single-cylinder port-fuel injection SI engine to quantify the potential of butanol/isooctane blends (with an alcohol concentration of 0%(vol), 25%(vol), 50%(vol), 75% vol and 100%(vol)) to reduce regulated pollutants (CO, CO2, Nox and THC), and non-regulated pollutants (methane, acetylene, ethylene, benzene, acetaldehyde and formaldehyde), without deteriorating the engine performance. A comparison with results obtained for ethanol/isooctane blends is given. It was observed that the addition of alcohol results in an increase of the fuel consumption of about 30% with butanol and 60% with ethanol, but only a slight increase (about 2%) in CO2 emissions. A strong decrease in HC and No-x emissions was obtained for both alcohols. For the non-regulated pollutants, the addition of ethanol induces a reduction of up to 100% in ethylene emissions, whereas with butanol, a strong increase is observed. The addition of butanol induces a greater decrease, of up to 100%, in methane emissions than ethanol. For benzene emissions, a strong reduction is observed for both alcohols. Moreover, the addition of alcohol engenders a reduction in acetylene emissions and an increase in formaldehyde emissions, but at different levels for both alcohols. Finally, no effects or trends were distinguishable for acetaldehyde and CO emissions. (C) 2011 Elsevier Ltd. All rights reserved.