Describes the API Test Laboratory Accreditation Program (PTLAP), a voluntary accreditation program open to all laboratories doing tests on petroleum products. The PTLAP objective is to verify the quality of test results from petroleum product testing. Describes the program requirements for laboratories that wish to be recognized by API as meeting specific industry requirements for testing, measuring, and inspecting petroleum products. Program participants must pass an on-site assessment before accreditation is awarded and must have an established quality system. Provides criteria for the qualification and selection of assessors, the conduct of on-site assessments, the evaluation of laboratories leading to accreditation, the continuance of accreditation, and the ongoing monitoring and surveillance of accredited laboratories.