Shubnikov-de Haas (SdH) oscillations are reported for well-characterized (single stage) encapsulated potassium (stages n=4,5,8) and rubidium (n=2,3,5,8) graphite intercalation compounds. Shapes of the Fermi surface (FS) are deduced from the dependence of the FS cross sections on the angle between the c-axis of the sample and H-->. The temperature dependence (1.4<T<=25 K) of the amplitudes of the SdH oscillations has been studied to find cyclotron effective masses for specific FS cross sections. A simple phenomenological energy-band model, based on the π bands of pristine graphite and c-axis zone folding, is used to calculate SdH frequencies as a function of Fermi energy and is applied to interpret the stage- and intercalant-dependent experimental SdH frequencies and effective masses. The good agreement between the observed and predicted effective masses and the FS cross sections confirms the general validity of this model.