Petroleum is a complex mixture of hydrocarbon compounds, usually containing impurities such as nitrogen, oxygen, sulfur, and small quantities of trace metals. The name petroleum comes from the Latin words for rock and oil, because petroleum was first found oozing out of rocks on the Earth's surface.

Ancient people discovered many practical uses for petroleum substances. According to the Old Testament, Noah waterproofed his Ark with pitch (natural asphalt), a very thick, glue-like form of petroleum. The Egyptians also coated their mummies with the sticky fluid to enhance preservation. Nearly 6,000 years ago, the people of Persia (now Iran) used petroleum substances as mortar in buildings and as a glue. Around 600 b.c., pitch was used to build the walls and pave the streets of Babylon. Primitive oil lamps were also commonly used by many ancient Middle Eastern and Mediterranean civilizations. On his way to China in the thirteenth...