We report on the effect of oxygen stoichiometry on the amorphous structure and crystallization kinetics of indium tin oxide. DC magnetron sputtering was used to deposit 200-nm-thick films under low, optimum (with respect to conductivity), and high oxygen partial pressures (0, 0.1 and 2 vol.%, respectively). The film stress and electron transport characteristics (hall mobility and carrier density) of these films were measured before, during and after the crystallization of 9.8 wt.% SnO2 doped In2O3. We report that the crystallization rate of films grown with oxygen contents above (2 vol.%) and below (0 vol.%) that required for optimum conductivity (0.1 vol.%) is reduced and that the as-deposited stress is, in all three cases, compressive and increases with increasing oxygen content in the sputter gas. In situ stress measurements were used to determine the change in molar volume attending both the crystallization of ITO and the oxidation of oxygen vacancies. Based on these measurements we report a measure of the effective volume of an oxygen vacancy in indium oxide.