Formulated for use in mixed fleets with diesel, CNG/LNG, and gasoline engines, the Phillips 66 Guardol NG-D 15W-40 engine oil is licensed for use in diesel-conversion natural gas-powered engines found in transit buses, school buses, delivery trucks, vans, and other vehicles. This engine oil is also API CK-4/SN licensed for use in traditional diesel applications and gasoline engines. This type of versatility allows mixed fleets to stock a single engine oil for all the vehicles they operate which saves time, inventory space, and money—while making regular maintenance easier.