Cover Story Flex Fuel Vehicles in the United States: Why Are We Lagging Behind Brazil? In Brazil, up to 90 percent of the drivers use flex fuel vehicles. In the States, it's 6 percent. What gives? Cover Story Water and Biofuels: Doing More with Less Biofuel production gets a lot harder when water is scarce, so researchers are busy with innovations Cover Story Drop-in Fuels: Game Changer in Biofuels? Directly replacing petroleum-based gasoline, diesel, and jet fuels would make commercially available drop-ins a major game changer Cover Story What Are Fuels? Jet engines require a continuous burn. Gasoline engines fire from spark ignition. Engine performance determines the fuel, and specifications set the standards. New fuels need to satisfy both.