The influences of ethanol and iso-butanol on gasoline engine performance, engine-out and tailpipe emissions were studied using a General Motors (GM) 2.0L turbocharged gasoline spark ignition direct injection (SIDI) engine. U.S. federal certification gasoline (E0), two ethanol-blended fuels (E10 and E20), and 11.7% iso-butanol blended fuels were tested. Fourier-Transform Infrared (FTIR) spectroscopy was used to measure non-regulated species including methane, ethylene, acetylene, formaldehyde, acetaldehyde, isobutylene, 1,3-butadiene, n-pentane, and iso-octane. A Fast Mobility Particle Sizer (FMPS) spectrometer was used to measure the particle number (PN) size distribution in the range from 5.6 to 560 nm. The regulated emissions total hydrocarbon (THC), carbon monoxide (CO), and oxides of nitrogen (NOx) were also measured. Both engine-out and tailpipe emissions results are presented as functions of alcohol content. In general, the alcohols tested reduced total PN emissions, with iso-butanol demonstrating the greatest reduction. Increasing ethanol content and iso-butanol increased formaldehyde emissions, with iso-butanol exhibiting the highest increase. Iso-butanol increased iso-butylene emission; however, it reduced emissions of 1,3-butadiene. Within the context of this study, the alcohols did not significantly change the other regulated emissions.