Variable angle reflectance FTIR spectroscopy was used to investigate the optical properties of indium tin oxide (ITO) and fluorine-doped tin oxide (SFO) thin films in the near-IR spectral region. The reflectance data were used to determine the plasma frequency and the electronic scattering time using the Drude free-electron model, the dielectric function of ITO, and the two- and three-phase Fresnel equations for reflection. The reflectance, plasma frequency, and electronic scattering time of ITO thin films were found to be dependent on the sheet resistance. Surface adlayers were also found to affect the reflectance and the position of the plasma frequency of the ITO thin films. The reflectance and observed plasma frequency for the SFO thin films were lower than those for any of the ITO films studied.