Abstract: Microbial oxidation of hydrocarbon gases can be divided into aerobic type and anaerobic type. Both of them can result in the enrichment of δ¹³C values of alkane gases. Some of the gaseous hydrocarbon components show priority during microbial oxidation. In general, propane and n-alkanes are usually preferentially oxidized as compared to ethane and iso-alkanes, respectively. And this has been confirmed by thermodynamics and culture experiments in anaerobic environment. Microbial oxidation can lead to partially reversed δ¹³C order, while component order does not reverse necessarily. But in some oxidation environments, ethane can be oxidized prior to propane. This means that the oxidation mechanism of aerobic oxidation is different from that of anaerobic oxidation or different type of microorganisms may lead to the change of priority during microbial oxidation.