Incorporates Addendum 1, 1998 - Describes the voluntary API Engine Oil Licensing and Certification System (EOLCS) and explains to marketers how different API marks are licensed and displayed for the consumer. The publication describes methods for developing new engine oil performance requirements and provides the marketer with a description of the API marks and their use, licensing requirements, aftermarket conformance, and enforcement procedures. EOLCS is the result of cooperation between the U.S. automobile manufacturers represented by the American Automobile Manufacturers Association (AAMA) and the U.S. petroleum industry represented by API. This program will benefit consumers, the petroleum industry and automobile manufacturers.