heading and tidy up
It is a heavy dark [[liquid]], consisting of many different [[hydrocarbon]] [[chemical compound|compound]]s. Wells are drilled deep in to the ground, and the crude oil is extracted and [[distillation|fractionated]] into its components by volatility in an oil refinery. Recent advances in drilling technology have enabled deeper and more difficult wells to be successfully drilled, allowing previously inaccessible reserves to be tapped.
Some of the main products distilled from crude oil are
: The following table<ref>Stainforth, J., Nourse, R. & Nosiara, M., 2007, ''Basin Oriented Geology - Petroleum Systems Module Course Manual''.</ref> compares the qualities of various types of petroleum: