Gear pumps are used for delivery of high-pressure fuel to aircraft engines. These pumps can suffer from erosion due to cavitation, which eventually causes an increase in leakage and reduced performance. An early warning of excessive wear is desirable, before the performance becomes unacceptable so that replacement can be scheduled conveniently without disrupting the operation of the aircraft. Pressure ripple and flow ripple measurements were performed on a range of fuel pumps with bearing conditions ranging from good to badly worn. The flow ripple was determined indirectly by analysis of pressure ripple measurements. Results suggest that there is a clear and fairly consistent increase in the pressure ripple and flow ripple measured at the high-pressure outlet port when the bearing is in a worn condition. This increase seems to occur at a wear condition that is not sufficiently bad to worsen the pump performance significantly. This measurement could provide a clear and simple indication of pump wear, at an opportune point in the wear cycle. However whilst these results look promising they are not conclusive, as other differences between the pumps may have affected the results.