Synthesis gas, or syngas, is a mixture of hydrogen, carbon monoxide, and carbon dioxide produced through gasification, reforming, or partial oxidation of carbon-heavy feedstocks such as crude oil residuum, bitumen, and waste biomass. Syngas became more commercially viable after the advancement of the Fischer-Tropsch process, which allows synthesis gas to be converted into diesel fuel. Synthesis gas gets its appellation from its use as an important intermediate chemical in the synthesis of synthetic natural gas, methanol, and ammonia.

Methanol, once known as wood alcohol, can be produced from synthesis gas with the use of catalysts. Methanol works as a solvent and can also be used to denature alcohol. While methanol can be condensed with catalysts to form olefinic and aromatic hydrocarbon compounds, it is predominantly oxidized to create formaldehyde, an important chemical in polymers and industrial resins.

While the three primary petrochemical groups are olefins, aromatics, and synthesis gas, certain alkanes, primarily obtained from natural gas processing plants, are also important feedstocks in petrochemical processing. These alkanes – specifically methane, ethane, propane, and butane – are straight-chain (not cyclic) saturated hydrocarbons. These colorless, odorless gases have a variety of uses. Methane, for example, is burned as fuel for electricity generation and heating. Propane is a clean-burning fuel used in heating and cooking applications. As a chemical feedstock, methane undergoes steam methane reforming to produce hydrogen gas in bulk. Ethane, when steam cracked, produces ethylene. Butane can serve as a feedstock for the production of ethylene and butadiene and is also used for gasoline blending and as a propellant in aerosol sprays.

Via the gas phase Haber-Bosch process, hydrocarbons can be synthesized into ammonia, a key component in fertilizers, pharmaceutical products, and cleaning chemicals.