Flex-fuel vehicles (FFVs) are designed to run on multiple types of fuel, primarily gasoline and ethanol blends, such as E85, which contains up to 85% ethanol. This flexibility allows drivers to choose the fuel that is most readily available or cost-effective, promoting the use of renewable energy sources. FFVs are equipped with special sensors and engine modifications that enable them to adjust to different fuel compositions automatically. This technology helps reduce greenhouse gas emissions and dependence on fossil fuels, contributing to a more sustainable transportation system.