Thin films of WO3 were deposited by DC magnetron sputtering at different oxygen partial pressures and different target surface oxidation states. Evaluation of the film properties was carried out using electrochemical and optical techniques. Electrochromic coloration efficiency is compared over a range of injected charge. Methods for determining the stoichiometry of the films are suggested. Excess electrochemically injected charge in the WO3 films is quantified and related to super-stoichiometry. Absorption measured in the as-deposited films is quantified and related to sub-stoichiometry. Deposition rate is an important consideration in the development of cost models for production of electrochromic devices. For many types of dielectric thin films deposited in in-line sputtering systems, the only concern is the onset of optical absorption. For WO3, many other aspects of the films' behavior may be affected. In this paper, ways to evaluate stoichiometry are examined in an effort to better understand the effect of changing process parameters on the films.