Improved experimental techniques were employed to measure the initial sputtering yields of condensed rare gas targets under 0.75-5 keV ion bombardment. These sputtering yields show a strong nonlinear dependence on the total stopping power. The experimental results for condensed Ar, Kr, and Xe targets are consistent with a systematic change from a linear collision cascade to evaporation and to a gas-flow mechanism as the deposited energy density increases. For condensed Ne sputtered by heavy projectiles. the yields are larger than can be explained by any existing quantitative model. The sputtering yields for all targets are found to approach a plateau values as sputtering progresses. This is attributed to surface roughening and the initial slope is used to determine the size of the impact damage area.