Spanish version is second edition with supplement ONLY. The purpose of this recommended practice is to provide standard procedures for the testing of oil-based drilling fluids. It is not a detailed manual on mud control procedures. It should be remembered that the agitation history and temperature of testing have a profound effect on mud properties. This recommended practice is organized to follow the tests as listed on the API "Drilling Mud Report" form (API 13G). Additional tests are given in the Appendix of this recommended practice.