(adj.) Geology. The quality of a source rock that makes it more likely to generate oil than gas. The nature of the organic matter (kerogen) in source rocks varies from coaly, plant-like material commonly found in terrestrial source rocks to algal or other marine material that makes up marine source rocks. Marine source rocks are commonly oil-prone. See: Gas-Prone, Generation, Hydrocarbon, Kerogen, Maturity, Source Rock