The origin of coal as a gas source and reservoir begins with peat and the mode of accumulation. Modern peatland analogs cover 2–3% of the world's landmass, yet are huge a carbon sink and source of greenhouse gases. Peatlands are grouped as marshes, swamps, and bogs based on ecological attributes and are controlled by hydrology, climate, nutrient supply, and external aquatic environments. Peatification produces gas whereby methanogens derive energy by converting carbon dioxide, hydrogen, formate, acetate, and other compounds from organic matter to either methane or methane and carbon dioxide. Peat gas, held below the groundwater table, is released by hydrostatic- and barometric-pressures fluxes. Peat accumulation and preservation occur in rapidly subsiding coastal, deltaic, alluvial, and lacustrine environments. Transformation of buried peat to fuel-grade coal and gas reservoirs is most likely to occur in thick tropical-bog deposits that continue to accumulate for >87,000 to >175,000 years subsequently compacted at peat:coal ratios of 4:1–13:1 forming lignite to anthracite coals.