The accumulation of natural gas in commercial volumes is a function of the dynamic equilibrium between its rates of generation and dissipation. It is proposed here that four fundamental factors control the formation of gasfields: two relate to generation, and two to dissipation. Details of these four factors are discussed. It is suggested that there exist plentiful supplies of ＇＇young＇＇ gas, located in relatively stable structural environments during post peak-generation stages, retained in place by efficient seals.