The change in work function of the (100) surface of a tungsten single crystal was measured as a function of time as gas adsorbed on the surface. Using a simple model, the work function changes for monolayer coverage were found to be 0.94 eV, −0.7 eV, 0.21 eV, and 0.44 eV, for O2, N2, H2, and CO2, respectively. The initial bare surface sticking probabilities were found to be 0.24, 0.37, 0.63, and 0.29, respectively. The initial changes in work function per molecule were found to be 9.4×10−16eV, −7×10−16eV, 2.1×10−16eV, and 1.75×10−15eV, respectively.