Picosecond pulse duration laser–material interactions are extremely complex and much less studied than the physics of femtosecond and nanosecond ablation. Additionally, multimode laser beam structure can inhibit robust analysis and comparisons of effects at any pulse duration. To address these gaps, single-pulse laser ablation of Al, Si, Ti, Ge, and InSb in air and Ge in vacuum was studied using low-transverse order Gaussian beams at a 1064 nm wavelength and 28 ps pulse duration. Crater depths of 0.4 to 6.3  μm and volumes of up to 4000  μm³ were measured using a laser confocal microscope. Crater depths plateau with increasing fluence and are slightly higher for Ge in vacuum than in air. Crater volume increases linearly with fluence for all materials in air. In vacuum, the volume of material above the surface was less than in air and increased at a lower rate with increasing fluence. The ratio of volume above the surface (due to melt flow and redeposition) to volume below the surface plateaus for all materials to ∼0.7 in air and 0.4 for Ge in vacuum. The ablation efficiency, defined as atoms removed per incident photon, was higher at low fluences and decreased to ∼0.004 for all materials at higher fluences. Simulations using the directed energy illumination visualization tool showed that bulk melt flow out of the crater caused by the evaporation recoil pressure dominated at higher fluences. Plateauing of crater depth with fluence was caused by melt reflow into the crater, which effects smaller crater widths more than larger ones, as evidenced by comparing multimode results with TEM₀₀ simulations. Recondensation of evaporated material was identified as the main difference between craters formed in air versus vacuum, and the Knudsen layer jump conditions in DEIVI were modified to account for an estimated ≈20  %   recondensation rate. The simulations showed a resulting reduction in evaporation, which created less recoil pressure, driving less melt out of the crater. The results of this study help elucidate mass removal mechanisms in the picosecond pulse duration regime and their dependence on laser and environmental characteristics.