It's all about price. Mineral based oil can be processed from soft coal, natural gas, and almost any grade of crude. Natural gas is so cheap right now due to the Barnett Shale formation in north Texas and a similar size discovery in the Dakotas. New drilling technology and fracking technology has expanded both the recoverable reserves, and the net volume per day. The eastern coal and oil reserves are on top of a lot of oil and natural gas once thought to be played out. Green weenies are doing everything they can to kill off fracking right now with a bunch of junk science on the earth crust and water tables. I don't care where the base stocks come from. The natural gas bases are easier to refine from my understanding.