An asymptotic analysis of the three-dimensional motion of a piston ring in its groove is presented, with appropriate nondimensional scaling. It is shown that the calculations in the literature use both a regular expansion and a multiple time scale expansion. The analysis is used to develop three ideas. First, the nondimensional parameters on which friction,F, and oil flow under the ring,Q, are identified. The variations ofFandQwith the nondimensional parameters are calculated. Second, it is shown that for normal wear on the second ring of a 2.6-L engine, there is a fivefold azimuthal variation inQ, suggesting that the azimuthal symmetry assumption must be relaxed, and that wear patterns must be taken into account in oil consumption calculations. Finally, a novel, gas-lubricated ring is described, and the variations inFandQwith nondimensional parameters calculated. Overall, it is found that the approach substantially simplifies the friction and oil consumption problem in reciprocating engines: for oil-lubricated rings,FandQvary with only four nondimensional parameters. For gas-lubricated rings,FandQvary with only three nondimensional parameters.Presented at the 39th Annual Meeting in Chicago, Illinois, May 7–10, 1984