A saturated aliphatic hydrocarbon that has the general formula C_nH_2n+2. Forming a homologous series, the smallest is methane (CH₄), followed by ethane (C₂H₆), propane (C₃H₈), butane (C₄H₁₀), etc. The smaller alkanes are gases at ambient temperature. Methane is found in oil and gas reservoirs, and in lesser amounts in coal seams. Methane is also the product of the decay of organic material by bacteria and produced from anaerobic digestion processes. Mixtures of short-chain alkane gases can be separated by distillation, either by condensing the liquids using low temperature or by pressurization, or a combination of the two. They were formerly known as paraffins although this name is still used in certain industries such as petroleum refining.