Changes

'''Petroleum''', named for "rock oil," is a [[fossil fuel]] usually found deep within the [[earth]], although some deposits are very close to the surface.   

'''Petroleum''', named for "rock [[oil]]," is a [[fossil fuel]] usually found deep within the [[earth]], although some deposits are very close to the surface.   

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.   

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.