In this Associated Press report , I read that, this week, Air New Zealand tested a passenger jet that was powered partially with oil from a plum-sized fruit known as jatropha (see photo below to get an idea of what a jatropha plant looks like). One engine of the Boeing 747-400 airplane was powered by a 50-50 blend of oil from jatropha plants and standard A1 jet fuel. The flight was a joint venture by Air New Zealand, airplane maker Boeing , engine maker Rolls Royce and biofuel specialist UOP , a unit of Honeywell International . Reading the article, I also learned that, besides jatropha plants, there are other promising biojet fuels such as switch grass, algae, and salt-tolerant plants called halophytes. Photo source