At eight locations (Illinois, Michigan, New York, North Carolina, Ontario, Quebec, Virginia, Washington) 'Gala' trees on eight rootstocks (P.1, M.26, O.3, B.9, Mark, M.9, MAC.39 and M.27) were replicated as 6-tree rows in four blocks. In-row spacing was 1.6 m and the trees were supported and trained to the HYTEC system. For each tree size and yield trait, there were significant site X rootstock interactions. At all sites, P.1 trees had the largest trunk cross-sectional area (TCA, cm2) and M.27 trees the smallest, and at most sites M.9, MAC.39, Mark, B.9 and 0.3 were similar. Also at most sites, Mark, 0.3 and B.9 had the highest yield per tree (kg) and M.27 and P.1 the lowest. Yield efficiency (kg/cm2 TCA) at all locations was lowest for P.1 and M.26 with only small differences among the other rootstocks. At sites with differences in mean fruit weight, P.1 had lower fruit weight than M.9.