Abstract Two experiments were made in which the true metabolizable energy (T.M.E.) values of various lipid materials were measured. Several fats had T.M.E. values greater than their gross energy values which suggests that fats may interact to allow increased utilization of the energy of other dietary components. The observed T.M.E. values of several fat mixtures were greater than the sums of the T.M.E. values of their component parts. High T.M.E. values were often associated with low levels of saturated fatty acids and high levels of dienoic acids; however, there were exceptions which lead to the conclusion that fatty acid composition as a predictor of T.M.E. may only be valid within certain groups of fats. The location of saturated fatty acids on the glycerol molecule was shown to affect T.M.E. values.