How does petroleum differ from natural gas?
Old liquid vs. old or new vapor.
Petroleum is a complex mix of liquid hydrocarbons created by the decomposition – usually under pressure over long times – of dead plants and animals. Natural gas is predominantly methane, also produced by organic material decomposition that was trapped underground. It also can be produced at low pressures and very short time-frames, as is done in the production of natural gas in landfills.