Flexible fuel vehicle production has been steadily increasing in the US over the past fifteen years. Ethanol is considered a renewable fuel additive to gasoline which helps the US efforts in minimizing the dependency on foreign oil. As a result, it is becoming very hard to find pure gasoline which does not contain some ethanol content at the pump in the US. The fuel currently available at the pump contains close to 10% ethanol. The fuel and evaporative systems components and materials on newer flexible fuel vehicles are being designed to be tolerant of the 10% ethanol content. There is a strong desire from ethanol producers to increase the ethanol content up to a 20% level. This is still being debated by the Environmental Protection Agency and a final decision has not been made yet but will be announced by the upcoming Tier 3 Notice of Public Rule Making (NPRM) in December of 2011. Early signs from EPA are indicating the E15 would be the official certification fuel with the upcoming Tier 3 NPRM. The California Air Resources Board (CARB) proposed in the LEV III NPRM to use E10 as the official fuel for all required certification testing.Many studies are being done investigating the impact of the 20% ethanol fuel blend on the different components in the vehicle especially on the evaporative systems. This study focuses on the effect of ethanol content on tailpipe emissions including carbonyls. The effect of ethanol addition to gasoline fuels on regulated tailpipe emissions is investigated under different ethanol content and different ambient temperatures. In addition to THC, CO, NOx, CH₄ and CO₂ tailpipe emissions, the analysis includes carbonyl measurement with formaldehydes, acetaldehydes, and other 11 carbonyl species. Testing was conducted on a 3.3 L Chrysler Town & Country vehicle at different ambient temperatures (20°F or -7°C, 50°F or 10°C and 75°F or 24°C) with indolene certification fuels containing 0, 10%, 20% and 85% ethanol. The effect of varying the Reid vapor pressure (RVP) on tailpipe emissions with E85 fuels is also discussed.