One of a group of organic compounds of carbon (C) and hydrogen (H) in which the carbon atoms have linear, branched chain (open), or both types of structures. Aliphatics, as they are informally called, can be divided into paraffinic (saturated) and olefinic (unsaturated) chain types. The simplest aliphatic, paraffinic hydrocarbon is methane, CH₄. The simplest aliphatic, olefinic hydrocarbon is ethylene, C₂H₆. In drilling fluids, particularly oil-base muds, the amounts and types of hydrocarbon in the mud can be an important parameter in overall performance of the mud.