Abstract Low energy electron diffraction and the Zisman modification of the Kelvin contact potential difference method have been used to follow the structural and surface potential changes during the adsorption of oxygen on the (110) surface of tungsten at temperatures of 300 and 80 K. Two chemisorbed states are formed at 300 K. The first of these exhibits a relationship between surface coverage, θ, and incident flux of gas atoms, closer to linear than a square law and a sticking coefficient of approximately 0.2. The second state, which begins to form at a coverage of half a monolayer, requires thermal activation and has a much lower sticking coefficient. At low temperatures (80 K) the first chemisorbed state is again formed and the work function versus incident flux is identical to that at 300 K up to θ = 0.5. At this coverage, unlike the 300 K state, the oxygen is not ordered. Beyond θ = 0.5 an electropositive state forms. It is readily desorbed by a 108 eV LEED beam or by heating. The characteristic energy of desorption has been measured to be 0.08 eV. Since this low binding energy and large positive surface dipole are similar to the corresponding values obtained for inert gas adsorption on tungsten single crystals, this state is considered to be one of physisorption.