Abiogenic petroleum origin is a term used to describe a number of different hypotheses which propose that petroleum and natural gas are formed by inorganic means rather than by the decomposition of organisms. The two principal abiogenic petroleum hypotheses, the deep gas hypothesis of Thomas Gold and the deep abiotic petroleum hypothesis, have been scientifically reviewed without confirmation. Scientific opinion on the origin of oil and gas is that all natural oil and gas deposits on Earth are fossil fuels, and are therefore not abiogenic in origin. Abiogenesis of small quantities of oil and gas remains a minor area of ongoing research.