A series of fatigue life tests on aircraft gear box size (45 mm bore) roller bearings were conducted with various aircraft gas turbine lubricants and with specific reference to Mil-L-7808 and variations thereof. It is shown that the 7808 lubricants generally cause a marked reduction in fatigue life as compared to that obtained with a medium viscosity mineral oil. It is also shown that lubricant bulk viscosity is a major factor in life. Subsequent testing demonstrated that the addition of thickeners to 7808 lubricants and formulations of this lubricant for a high Ryder Gear Rating are not effective in raising the fatigue life. It also appears that the SOD lead corrosion test is not pertinent in bearing life. Suggestion is made that the 7808 specification be relaxed to allow of higher viscosity for heavily loaded bearings as in gear boxes.Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Toronto, Canada, October, 1957.