Natural gas is found in deep underground natural rock formations or associated with other hydrocarbon reservoirs in coal beds.Most natural gas was created over time by two mechanisms: biogenic and thermogenic. Biogenic gas is created by organisms in marshes, bogs, landfills, and shallow sediments. Deeper in the earth, at greater temperature and pressure, thermogenic gas is created from buried organic material.Before natural gas can be used as a fuel, it must undergo processing to clean the gas and remove impurities including water to meet the specifications of marketable natural gas.