The effects of multiple phase-transitions on the dynamics of the Venusian mantle have been investigated with a two-dimensional finite-element method. A depth-dependent thermal expansivity has been employed in a purely basal heating configuration with an aspect-ratio of four. The addition of the olivine→ spinel transition promotes layered convection more so than models with a single spinel→perovskite phase-change. The shifts in the phase-transition depths and the presence of a conductive lid increase the tendency of the Venusian mantle circulation to flow through the transition zone. The potentially lower Rayleigh number in Venus from lack of volatiles will also enhance whole mantle convection. The style of convection in Venus may have changed from layered convection in the past to whole-mantle convection today. This transition might have been responsible for the major resurfacing event on Venus. ¿ American Geophysical Union 1992