Fossil feedstocks are mixtures
Natural gas, crude oil, and coal formed through long geological processes from earlier organic matter, but they are chemically different materials. Natural gas is a gas mixture usually rich in methane, with variable ethane, propane, butanes, nitrogen, carbon dioxide, water vapour, and sulfur-containing impurities. Crude oil is a complex liquid mixture of hydrocarbons and smaller amounts of other compounds. Coal is a carbon-rich heterogeneous solid containing hydrogen, oxygen, nitrogen, sulfur, minerals, and moisture; it is not pure carbon.