Pendimethalin and sulfentrazone are applied PRE in sunflower to control many grasses and broadleaf weeds. These herbicides have quite different physicochemical properties. Pendimethalin has a high carbon-referenced sediment partition coefficient (Koc)(17,200 L kg−1), with a low leaching potential, whereas sulfentrazone has a low Koc (43 L kg−1), with a high leaching potential. A 2-yr study was conducted to determine the dissipation of these two herbicides applied to a loamy sand soil. Pendimethalin dissipated in two phases, an initial rapid loss between application and 3 to 5 d after application (DAT) and then a slower rate of dissipation. The first, rapid phase was likely due to volatilization of the herbicide from the soil surface. Pendimethalin dissipated at a similar rate for the slower phase in 2008 and 2010 (time to 50% dissipation [DT50] was 43 d and 39 d, respectively). The dissipation of sulfentrazone, unlike pendimethalin, was not biphasic. The DT50 for sulfentrazone was different between the 2 yr (30 d and 14 d in 2008 and 2010, respectively). Pendimethalin remained primarily in the top 7.5 cm of the soil column, whereas sulfentrazone leached to at least 30 cm. The leaching of sulfentrazone depended on the timing of irrigation or precipitation after application. The more rapid loss of sulfentrazone in the top 30 cm of the soil column in 2010 could have been partially due to the herbicide leaching below the 30 cm depth that was sampled.