Tin doped indium oxide (ITO) films with a few mol% of silver were prepared by reactive DC magnetron sputtering. The purpose of adding silver is to boost conductivity. The real part of the refractive index of ITO was determined from ellipsometry data, applying a model combining a Drude and a Lorentz term. The imaginary part was calculated from the absorptance, which was derived from transmittance and reflectance data. We found that up to 6 mol% of silver additive enhanced the conductivity by as much as a factor of two for layers post-treated at 200 and 300 degreesC in reducing gas consisting of 93% N-2 and 7% H-2. For samples with 1 mol% silver, which was post-treated at 100 and 200 degreesC, we observed an increase in the luminous transmittance. The transmittance decreased with increased silver content.