Alternative fuels have received considerable attention since the early seventies with alcohol being initially most prominent. In particular ethyl alcohol seemed very attractive because of possible on-farm production and the renewable source material. Because alcohol is not a very suitable compression ignition fuel, plant oils began to be investigated as alternative fuels. It was shown that these oils cause coking of the injector nozzles in direct injection engines and esters of plant oils were tested as a possible solution to the problem. From these tests fuel properties were determined and specifications derived. Combustion studies were carried out and compatability tests performed. Engine durability was tested under a manufacturer's prescribed cyclic load conditions over a period of 1500 hours with extremely good results.