THE NATURE OF THERMOGENIC GASES Thermogenic gases are generated by abiogenic decomposition of organic matter in sediments, largely driven by geothermal heat associated with deep burial. Com­ plex organic compounds are reconfigured into simpler gaseous and liquid prod­ ucts and solid residue. Products of abiogenic decomposition include coal, crude oil, methane and higher hydrocarbon gases, and carbon dioxide. Gaseous and liquid products may be expelled from organic-rich sediments into surrounding strata.