Heat effects in lubricating films are analyzed on the basis of simple shear of the lubricant, Reynolds logarithmic formula relating lubricant viscosity and temperature, and an equation relating the heat generation and heat flow in the film. The film-temperature dependence on velocity is determined, and the result is used to obtain the shearing stress and shearing rates. The formulas thus derived are useful in analyzing the performance of oil-film bearings. Experiments have been carried out with measurement of shaft- and bearing-surface temperatures, as well as friction; the tests support the analytical results. An approximate means for judging the importance of film heating in a given case in terms of velocity and lubricant viscosity is suggested.