A physical mechanism for in situ forcing of the Venus thermospheric superrotation is developed, which is in accord with the bulk of the constraining observations. Saturation of small- to medium-scale internal gravity waves in the thermosphere can supply the necessary accelerations of the mean flow if the waves have predominantly large westward phase speeds, characteristic of the wind speeds in the upper clouds. Several scenarios for wave forcing are examined, and the Lindzen-Holton parameterization is used to derive wave-induced acceleration of the mean flow. The results are compared to the VTGCM, which uses a similar wave drag parameterization with an ad hoc (empirically based) asymmetry parameter to model the superrotation. ¿ American Geophysical Union 1992