There has been increasing interest in recent years in the use of biodiesel as a substitute for petroleum-based diesel fuel. Biodiesel is a renewable alternative fuel produced from a wide range of vegetable oils and animal fats and even recycled grease and works in conventional diesel engines, with one major exception - biodiesel significantly reduces harmful emissions. In the developing world, biodiesel is produced from palm oil, sunflowers, and other sources. In Indonesia, there is significant concern that biodiesel may be causing deforestation, as native forests are removed to make way for palm oil plantations. Biodiesel is one of many alternative fuel options that has the potential to help reduce oil dependence and global warming pollution. It is now a recognised fuel and can generally be used as a straight substitute for standard diesel. Otherwise, biodiesel is beginning to make its way into the aviation jetfuel market, several flights have already been made using various biofuel combinations.