Hyne N.J. Nontechnical Guide to Petroleum Geology, Exploration, Drilling and Production

2nd edition. — Pennwell Books, 2001. — 575 p. — ISBN: 087814823X.Both crude oil and natural gas are mixtures of molecules formed by carcarbon and hydrogen atoms. There are many different types of crude oils and natural gases, some more valuable than others. Heavy crude oils are very thick and viscous and are difficult or impossible to produce, whereas light crude oils are very fluid and relatively easy to produce. Less valuable are sour crude oils that contain sulfur and sour natural gasses that contain hydrogen sulfide. Some natural gases burn with more heat than others, contain natu- natural gas liquids and gasoline, and are more valuable.