Jojoba oil is actually extracted from the wax in the beans of the Jojoba plant. To do so, the wax has not only to be heated to its melting point, but then the "oil" has to be filtered, and treated so that it remains " thin" at normal temperatures. To that extent, the plant oil is processed, and therefore synthetic.
However, other oils are synthesized from chemicals, rather than from petroleum, or plants. Synthetic oils, and fuels were studied extensively as a national defense issue during WWII, by both Germany, and here in America. Synthetic fuels can be made, but the oil companies have been able to keep the price of oil based gasoline and diesel fuel low enough that these alternative fuels have not seen commercial use. Where you see extensive use of synthetic oils is in the airline industry, because of the extreme range of temperatures those oils have to survive in keeping those engines working.