A recent study of spent cooking oil by Gerhard Knothe and Kevin Steidley in Bioresource Technology showed that this resource is highly variable in nature. The variability comes from different kinds of oil being used by different restaurants under varying conditions. Oil that is used for longer time periods or heated to higher temperatures will have different resulting composition of the fuel. Overall the survey of the properties of various samples of vegetable oils indicated their viability as a fuel source even though the higher cloud and pour points of the cooking oil decreased its low-temperature performance as a fuel. The viscosity of the cooking oil places it in the right range for American biodiesel use and selective European biodiesel use. Finally they determined that due to the varied properties of cooking oil tests would need to be run on the oil to determine the amount of processing need to take place to make it into a viable biodiesel.
Cooking oil is a highly variable feedstock for biofuel