Pentadecenoic is high purity monounsaturated fatty acid which is optimal as a standard and for biological systems. It has a cis double bond at an even carbon (carbon 10) and thus cannot be enzymatically degraded by the usual beta-oxidation pathway. Rather, a reductase-isomerase or an epimerase pathway must be occupied in the metabolism of this fatty acid. Pentadecenoic acid (cis-10) is not usually found in nature and accordingly a good monounsaturated internal standard.