The electronic effects produced by controlled gas exposures on alpha-sexithiophene thin films have been investigated using x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Incremental exposures of alpha 6T films to NO2, O-2, NH3 in N-2, and water vapor in N-2 were performed in ultrahigh vacuum, while repeated doses of O-2, H-2 in N-2, and methanol vapor in N-2 were performed ex situ at ambient pressure. In both conditions XPS spectra of gas-exposed films showed no evidence of chemical changes. However, the features in both XPS and UPS spectra were observed to shift as a function of gas dosage, with the magnitude dependent on each particular gas. These effects could be reversed by heating the films to temperatures around 100 K. This behavior is interpreted in terms of doping by weakly bonded gas species within the near-surface region of the alpha 6T films. Greater doping effects were observed for films dosed at ambient pressure. We discuss possible gas adsorption models that may explain the differing gas sensitivities and their dependences on pressure, temperature, and exposure lime. Finally, temperature programmed desorption was used to study the reversibility and resistance to reaction of a6T films during this gas adsorption/desorption process. The films were found to be chemically stable to gas exposure and subsequent thermal desorption in the dosage ranges explored.