A term used to describe source rock that mainly generates gases rather than oil. Gas-prone source rock is usually sourced from terrestrial organic matter that is derived from plant materials. Source rocks, such as coal tends to be gas-prone. Gas source rocks usually have lower quality organic matter and lower amounts of TOC than oil-prone source rocks (except for coals that have high to very high TOC) and thus hydrogen indices that range from (100-~250) mgHC/gTOC. Gas-prone organic matter is known to identify with Type III kerogen.