a b s t r a c tSeven wear tests were conducted on an FZG gear testing machine in order to ascertain the influence of basestock (PAO and mineral), specific film thickness and contact load on the wear of spur gears, particularly on the wear coefficient κ that is used in Archard's law. The results showed that load may have some influence on the wear coefficient. They also showed that the influence of specific film thickness on wear is very non-linear. The influence of basestock, even with oils of similar viscosity, is very significant, as much as any other parameter in isolation.