Using a transit‐time technique, we have measured domain‐wall velocities versus applied fieldHfor Bloch, Neˆel, and the head‐to‐head walls in bulk single‐crystal bars of yttrium orthoferrite from 150 to 600 °K. Fields as high as 100 Oe were applied and wall velocities exceeding 106cm/sec were recorded. After correcting for magnetostatic effects, all three walls display a well‐defined linearv‐Hregion, with a common mobility &mgr; of 1.2×104cm/sec Oe at 300 °K. As a function of temperatureTthe wall mobility varies as 1/T2. From these results it is argued that the mobility arises from thermal spin‐wave scattering. Velocities for the three walls become field independent abruptly atvs=4.2×105cm/sec and maintain this velocity untilHexceeds ∼60 Oe, whereupon the velocity again increases. We demonstrate that this ’’saturation’’ atvsis due to the interaction between the wall and the bulk acoustic phonons.