A calcium soap of naphthenic acids in crude oil. Naphthenates are formed through interaction of naphthenic acids in crude oil with metal ions such as calcium and sodium. Insoluble in either the oil or water phase, and with a density between that of oil and water, naphthenates tend to accumulate at the oil/water interface and act as surfactants to help stabilize emulsions. Naphthenates can also be deposited as solids in pipelines, and can cause flow-assurance problems.