1. Performance Level
Motor oils designed for cars, vans, and light trucks fall under API’s “S” (Service) categories. Motor oils designed for heavy-duty trucks and vehicles with diesel engines fall under API’s “C” (Commercial) categories. Please see the Gasoline Engines and Diesel Engines charts for descriptions of current and obsolete API service categories.

2. Viscosity Grade
The measure of an oil’s ability to flow at certain temperatures. Vehicle requirements may vary. Follow your vehicle manufacturer’s recommendations on SAE oil viscosity.

3. Resource Conserving and Energy Conserving
These designations apply to oils intended for gasoline-engine cars, vans, and light trucks. Widespread use of “Resource Conserving” or “Energy Conserving” oils may result in an overall savings of fuel in the vehicle fleet as a whole.

4. Multiple Performance Levels
Oils designed for diesel engine service might also meet gasoline engine service. For these oils the designation is “C” category first followed by the “S” category. “C” category oils have been formulated primarily for diesel engines and may not provide all of the performance requirements consistent with vehicle manufacturers’ recommendations for gasoline-fueled engines.

5. The API Service Symbol with CI-4 Plus
The “CI-4 PLUS” designation identifies oils formulated to provide a higher level of protection against soot-related viscosity increase and viscosity loss due to shear in diesel engines. When originally introduced, CI-4 PLUS identified CI-4 oils meeting a higher level of performance. CJ-4 oils include all CI-4 PLUS performance requirements. CI-4 PLUS appears in the lower portion of the API Service Symbol “Donut.”