The most widely used standard tests for the evaluation of wear and extreme pressure properties are analysed in terms of eight tribological parameters. Wide variations in the test conditions are disclosed and the over-riding influence of thermal conditions on test severity is made clear. The relation between tests, such as the Timken, in which one of the two rubbing surfaces is static, and gear or cam and follower tests in which both specimens move, is explored. A preliminary account is given of a new test procedure evolved as a result of the study.