Any of a number of fluids (liquids) manufactured from starting products of known composition and purity. Popular fluid types include several olefin oligomers of ethylene. Esters made from vegetable fatty acid and alcohol were among the first such fluids. Ethers and polyethers, made from alcohols and polyalcohols, have been used, along with paraffinic hydrocarbons and linear alkyl benzenes. Mixtures of these fluids are also used to make synthetic-base muds.