Petroleum Coke Overview. Petroleum coke (petcoke) is one of many valued consumer products produced during the oil refining process. Crude oil is processed into gasoline, diesel fuel, jet fuel, lubricating oils and waxes, leaving some residual crude that usually undergoes additional processing. Residual fuel oil use (petcoke is used to make residual fuel oil) in the U.S. has been declining for decades because natural gas and coal are much more economical fuels to use in industrial applications and power generation. In 2012, petcoke accounted for just 0.2 percent of U.S. power generation.