The document discusses various alternative fuels that could potentially replace gasoline and diesel in the future due to concerns over depletion of fossil fuels and harmful emissions. It describes some of the key alternative fuels like ethanol, methanol, vegetable oils, biodiesel, hydrogen, and gases. Ethanol shows promise because it can be produced from agricultural waste at low cost and reduces harmful emissions from engines. The document also discusses the various ways these alternative fuels can be used in engines and their advantages and disadvantages. Overall, it examines the need to shift to alternative fuels and provides an overview of some of the most promising options.