The effect of gas turbine engine lubricant viscosity on rolling contact fatigue (RCF) life was studied using four fully formulated synthetic ester based lubricants with the same additive package. The lubricants were evaluated using a modified ball-on-rod type rolling contact fatigue tester for fatigue and wear characteristics, at a maximum hertzian stress of 4.8 GPa and at a speed of 3600 rpm. Weibull analysis and analysis of variance (ANOVA) were performed on the data to determine any significant difference in performance. The lubricant deposits formed at the tribocontact were examined by Auger Electron Spectroscopy (AES). At ambient temperature, viscosity had no effect on both RCF life and wear. However, at 177°C the higher viscosity lubricants formed thicker lubricant film deposits and showed superior fatigue life and reduction in wear rate.