Increasing demands of high speed, heavy duty, and small size for a gear device promote the bulk temperature rise in gear teeth. The temperature rise affects both bending strength and surface durability of the gear teeth as well as the scoring resistance and causes a decrease in accuracy of the gear device due to thermal expansion. To establish an effective lubrication method for ultrahigh-speed gears, this study aims at determining an optimum centrifugal lubrication method to cool spur gear teeth. In this paper, on the basis of the observation of oil jet behavior, we proposed a new centrifugal lubrication method in which oil is injected through a hole drilled on the tooth crest. Oil jetted out from a gear splashes after striking against both addendum and dedendum flanks of a mating gear. A multiple regression equation for estimating the flow rate of oil jetted out through a hole was obtained by dimensional analysis and experiments.