Engine oil service classifications are standardized by which of the following organizations?

The correct answer is that engine oil service classifications are standardized by the American Petroleum Institute (API). The API sets the specifications for engine lubricants, ensuring they meet certain performance criteria and quality standards necessary for various types of engines, particularly in automotive and industrial applications. This includes the development of service categories that help consumers and mechanics choose the appropriate oil for specific engine types and conditions.

The SAE (Society of Automotive Engineers) primarily provides classifications related to viscosity grades of oils but does not set service classifications. ASTM (American Society for Testing and Materials) focuses on developing standards for materials and products in a broader sense, while ISO (International Organization for Standardization) develops international standards across various fields but is not specifically tasked with engine oil classifications like the API. Therefore, the API is the key organization recognized for engine oil service classifications.