Natural-gas processing at ambient conditions (i.e., pentane and heavier) are called "natural-gas condensate" (sometimes also called "natural gasoline" or simply "condensate"). Natural gas is called "sweet gas" when relatively free of hydrogen sulfide; gas that does contain hydrogen sulfide is called "sour gas". Natural gas, or any other gas mixture, containing significant quantities of hydrogen sulfide, carbon dioxide or similar acidic gases, is called "acid gas." Raw natural gas can also come from methane deposits in the pores of coal seams, and especially in a more concentrated state of adsorption onto the surface of the coal itself. Such gas is referred to
Natural gas prices import gas based on the Henry Hub index, which was, until very recently, the most widely used reference for US natural gas prices. Depending on the marketplace, the price of natural gas is expressed in US dollars (or other currency) per 1 million British thermal units (MMBtu), thousand cubic feet (Mcf), or 1,000 cubic meters. Note that, for natural gas price comparisons, $ per MMBtu multiplied by 1.025 = $ per Mcf of pipeline-quality gas, which is what is delivered to consumers. For rough comparisons, one million Btu is approximately equal to a thousand cubic feet of natural gas. Pipeline-quality