A statistical investigation of the operating slip/twinning modes and their interactions at grain scale over a large area, containing ~400 grains, was carried out on rolled Mg sheets during room-temperature compression based on EBSD and slip trace analysis. For 10% strain, the slip mode was dominated by basal slip (89%). All the 363 identified twins were tension twins. The concave-up stress-strain curve indicated a twinning-dominated deformation behavior, which was further confirmed by the large twinned area fraction (41%) after the deformation. Most twin variants (79%) followed the Schmid law. The Luster-Morris parameter (m'''') did not correlate well to twin transmission. However, most twin transmissions (82%) exhibited larger normalized m (Schmid factor) and m'''' values. Additional slip systems were frequently active in the twin domains while not in the parent, which can be explained by Schmid law. Slip transfer across the twin boundaries was also observed. Statistical m analysis revealed that twinning activity was closely related to prismatic slip.