Because of domestic production from renewable sources and their clean burning nature, alcohols, especially ethanol, have seen growing use as a blending agent and replacement for basic hydrocarbons in gasoline. The increasing use of alcohol in fuels raises questions on the safety of these fuels under certain non-operational situations. Modern vehicles use evaporative emission control systems to minimize environmental emissions of fuel. These systems must be relatively leak-free to function properly and are self-diagnosed by the vehicle On-Board Diagnostic system. When service is required, the service leak testing procedures may involve forcing test gases into the “evap” system and also exposure of the fuel vapors normally contained in the system to atmosphere. Previous work has discussed the hazards involved when performing shop leak testing activities for vehicles fuelled with conventional hydrocarbon gasoline [1, 2]. Oxygenate-blended fuels have significantly different vapor behaviors than conventional gasoline, and these changes affect the flammable mixture hazards associated with leak testing procedures.This paper discusses the relevant vapor/liquid equilibrium and vapor properties of various oxygenate fuels and examines how these affect the flammable mixture hazards associated with shop leak testing procedures for fuel systems containing high oxygenate blends. The emphasis is on E85 as the most common currently used alternative fuel. A simple binary hexane-ethanol model was used to predict the equilibrium fuel vapors that are present in the fuel tank vapor space during shop leak testing with E85 present. The model was compared to experimental results that included the effects of weathering. The hazard associated with other oxygenated fuels could be predicted using previous literature. The results show that the vapor flammability hazards of oxygenate-blended gasoline fuels during leak testing activities are initially similar to those from conventional gasoline. However, the potential effects of fuel weathering during shop testing and of anomalous temperatures are significantly more severe for some oxygenated fuel blends, particularly the high alcohol blends including E85.