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The focus of this study was the characterization and comparison of power-specific exhaust emission rates from a closed-loop small spark-ignited engine fuelled with ethanol and isobutanol gasoline blends. A 4-cycle Kohler ECH-630 engine certified to the Phase 3 emissions standards was operated over the G2 test cycle, a six-mode steady-state test cycle, in its original configuration. This engine was equipped with electronic ignition, electronic fuel injection and an oxygen sensor. Certification gasoline fuel was splash-blended by percent volume with ethanol and isobutanol to result in the test blend levels of E10, E15, iB16 and iB8-E10. Reductions in emission rates of carbon monoxide (up to 12.0% with the ethanol blends and up to 11.4% with the isobutanol blends) were achieved along with a reduction in total hydrocarbons (up to 10.9% with the ethanol blends and up to 8.2% with the isobutanol blends). Nitrogen oxide emissions were decreased by up to 9.8% with the ethanol blends.