We report on the dependence of the sticking coefficient S of O-2 on Ag(110) on oxygen coverage, for molecular and dissociative adsorption. S is found to diminish strongly with increasing coverage. The initial dependence is linear and for dissociative adsorption the slope depends on crystal temperature. The data are indicative of a coverage dependence of the adsorption barrier height, which is caused by the change of the surface work function with coverage. The analysis of the temperature variation of the dependence of S on coverage allows to extract the variation of the ratio of the pre-exponential factors and of the height of the barriers for desorption and dissociation from the molecularly chemisorbed state.