Bubble collapse times were determined as a means to characterize wall velocity vs. drive field in thin (3 to 11 &mgr;m) epitaxial garnet films of compositions near Y3Ga1Fe4O12, Eu0.5Y2.5Ga1Fe4O12and Gd0.5Y2.5Ga1Fe4O12. The results resemble that reported for thick platelets ( > 25 &mgr; thick) with large diameter bubbles ( d ≈ 25 &mgr;). An initial steep slope (∼103cm/sec‐oe) is followed by a curve of diminishing slope. The deviation from linearity occurs well below Walker's limit of velocity Vw= 2&pgr;&ggr;Ms▵valid for free wall motion in a plate of infinite thickness. Our theory shows that when damping (Gilbert'sa) is small, stray fields near the film surface destabilize the linear uniform motion. At fields above the limit Hc= 9. 5ax (2&pgr;A)1/2h−1irregular Bloch line motion occurs and the mean wall velocity approaches the asymptoteVo = 7.1 &ggr;Ah−1K1/2To the extent that experimental knee velocities are well defined, they range from 1/2 to 1 times Vo.