is an engine oil categories developed by SAE, ASTM, and API, based on an oil’s fuel-saving performance in passenger cars, vans, and light trucks. An "Energy Conserving" oil must produce a fuel economy improvement of 1.5% or greater over a reference oil in a standard ASTM test procedure. An "Energy Conserving II" oil must produce a fuel economy improvement of at least 2.7%. In actual vehicle operation, the fuel economy obtained by these lubricants may differ, depending on vehicle type, operating conditions, and driving habits.

Also see fuel-economy oil.