Novel zero-phosphorus engine oils have been developed which are based on the use of combinations of copper and sulphur compounds. Bench oxidation tests have shown that copper oleate and a sulphurised ester provide better oxidation and viscosity control than can be obtained with zinc dithiophosphates when used in combination with either soluble copper compounds or aromatic amines and hindered phenols. The good bench test results were confirmed in the Sequence IIID engine test where excellent control of viscosity was obtained. These oils, in some cases also containing a borate ester, performed well in the CRC L-38 bearing corrosion test and also provided good wear protection in a motored rig test and in the Sequence IIID test. Field testing of the oils developed in this work showed that they provided satisfactory performance under normal driving conditions.