An improved model of Venusian global gravity has been obtained by fitting an eighteenth-degree and eighteenth-order spherical harmonic series to 78 orbital arcs of high altitude (950--1350 km at periapsis) tracking data and 351 orbital arcs of lower-altitude (150--200 km at periapsis) data from the Pioneer Venus Orbiter (PVO). Compared to a recently published tenth degree model Mottinger et al., 1985>, which is based on the 78 high-altitude arcs only, the current model provides a significant improvement in resolution and fidelity. As a measure of this improvement, we note that for the low-altitude arcs alone, the variance of the residuals for the present model is reduced to 19% of the data variance, compared to 51% for the tenth-degree model. Venus differs significantly from the Earth in that it exhibits a significant correlation between long-wavelength topography and gravity. The gravity/topography spectral admittances are inconsistent with either Airy or Pratt isostasy, but they are consistent with dynamic support by mantle convection. ¿American Geophysical Union 1987