The paper is a brief review of the research on fundamentals of gear lubrication performed at Shell Development Company for the Bureau of Aeronautics of the Department of the Navy. It is constructed along the following lines: Scoring and wear of gears are evaluated as functions of various operating variables, gear geometry and construction factors, and lubricants properties. This is followed by a brief discussion of the results of experiments performed with tagged extreme pressure lubricants showing distribution and thickness of the extreme pressure films and the rates of their attrition. Based on all of these results, a mechanism of gear lubrication is postulated and discussed.