Both monolayer and bilayer periods are observed during the growth of germanium on Ge(1 0 0) using reflection high-energy electron diffraction (RHEED). Oscillations in the specular beam intensity of the RHEED pattern are recorded for substrate temperatures of 400-850 K over a wide range of incident germanium fluxes. With careful sample preparation, the period of the RHEED oscillations consistently goes through a transition from a bilayer period to an alternating intensity monolayer period as the surface temperature is raised above similar to 700 K. Without this preparation, only bilayer periods characterized by symmetric-shaped oscillations are observed. This indicates that the sample preparation plays a key role in determining the resulting growth. The period of the RHEED oscillations is not strongly dependent on the incident angle of the electron beam, suggesting that the observed periods are not a result of a diffraction condition, such as Kikuchi lines. The data are consistent with a mobility-controlled dynamic bilayer versus monolayer growth mechanism.