A synthetic fuel gas is produced from crude oil by a combination of inter-related steps which separate the oil into several fractions, a first ethane and lighter gaseous fraction, a further gas fraction containing propane and butane, a gasoline containing fraction boiling up to, about 400* F, and a heavy oil or residual fraction, the first two fractions are treated with caustic to remove sulfur and sulfur compounds therefrom, the third fraction is hydrodesulfurized and the fourth fraction is catalytically cracked to extinction to produce gaseous products and an additional gasoline fraction which is hydrodesulfurized whereupon all except the first fraction are combined and then converted by known operation to produce a synthetic natural gas or fuel. This gas or fuel can be combined with the first gas fraction either before or after hydrogen has been removed from it.