Description Mobil Delvac 1 ESP 5W40 is the premium high performance diesel engine oil in the Mobil line-up. Delvac 1 ESP is a full synthetic diesel engine oil designed for long service, ultimate friction and wear control, and has the ability to provide improved fuel economy. Mobil Delvac 1 ESP is especially engineered for modern low emission diesel engines especially those designed to operate with SCR technology utilizing Diesel Exhaust Fluid.