Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In chemistry, a partial oxidation (POX) reaction occurs when a substoichiometric fuel-air mixture is partially combusted in a reformer, creating a hydrogen-rich syngas, which can then be put to further use, for example in a fuel cell. A distinction is made between thermal partial oxidation (TPOX) and catalytic partial oxidation (CPOX).Partial oxidation is a technically mature process in which natural gas or a heavy hydrocarbon (heating oil) is mixed in an exothermic process with oxygen.