This study presents water-tunnel experiments on the interaction between two staggered ventilated supercavities, focusing on asymmetric cavity morphology, critical ventilation demand, and closure-mode transitions induced by a streamwise offset. The transverse spacing ratio is fixed at LH/DC = 5.3, while the streamwise spacing ratio LV/DC = 0, 1.67, and 4 over a range of Fr and CQ. A robust asymmetric mode is found: the gap-side interface of the upstream cavity is compressed and flattened, whereas that of the downstream cavity expands toward the gap passage and is likewise flattened. This asymmetry is attributed to the streamwise offset breaking the symmetry of pressure recovery near the closure region, driving the closure region to a new equilibrium location. Critical formation and collapse coefficients (CQf and CQc) are quantified using two ventilation protocols. In case 1, CQf and CQc exceed the single-cavity thresholds at low Fr owing to the downstream stagnation high-pressure region, but become lower as Fr increases; both increase with LV/DC. In case 2, the critical thresholds are reduced because the upstream stagnation high-pressure region does not directly elevate Pout near the closure region. These trends are interpreted using the dimensionless pressure difference across the gas–liquid interface. Three closure modes are observed: foam cavity, hybrid foam cavity and re-entrant jet (FCRJ), and twin vortex (TV). Relative to the single-cavity condition, the TV regime expands, while the FCRJ regime contracts slightly, and the TV regime shrinks with increasing LV/DC.