has increased levels of derives from derives into sulfur molecular entity petroleum planktonic material hydrocarbon gas kerogen planktonic kerogen Kerogen which is enriched in sulfur compounds, has a hydrogen to carbon ratio under 1.25, an oxygen to carbon ratio between 0.03 and 0.18, derives into mixtures of hydrocarbon gas and oil, and derives from marine organic materials (primarily lipids) which are formed in reducing environments.