Crop farmers are understandably interested in use of vegetable products as petroleum substitutes. Much of this interest now centers around fuels for internal combustion engines . Use of "raw" or slightly modified seed oils as diesel fuel is attractive for a number of reasons: 1) oil extraction is a rather simple , straight-forward process; 2) the high-protein by-products are already being used in commercial animal feed supplements ; and 3) energy and dollar cost balances are easily calculated, and seem to favor on-farm processing .