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Recent laboratory and field studies indicate that the P-wave velocity in Athabasca tar sands decreases when temperature increases during steam injection. In this paper we derive time variant velocity models from seismic traveltime inversions of both reflection and borehole data. Prior to steam injection, three‐dimensional (3-D) reflector velocity‐depth models are established using image‐ray conversions of traveltimes to depth. The changes in velocity due to steam injection are modeled by inverting traveltime data from seismic monitor surveys after steam injection and comparing these results to velocities computed prior to steam injection. Velocity models are essentially determined by traveltimes from the 3-D seismic reflection survey. The surface‐to‐wellbore data traveltimes show the expected delay caused by steam injection but do not significantly alter the velocity model produced by reflection traveltimes. For seismic monitor surveys, low‐velocity zones show a very good correlation with zones of temperature increase at injector well positions. The results indicate that velocity models obtained from seismic traveltimes may prove useful in detecting steam fronts in tar sands.