A fatty acid with the active hydrogen replaced by the alkyl group of a monohydric alcohol. The esterification of a fatty acid, RCOOH, by an alcohol, R′OH, yields the fatty ester RCOOR′. The most common alcohol used is methanol, yielding the methyl ester RCOOCH3. The methyl esters of fatty acids have higher vapor pressures than the corresponding acids and are distilled more easily.