A vehicular rear window assembly for a vehicle comprises a first fixed pane, a second fixed pane, and a sliding pane, which is supported for horizontal movement between open and closed positions. The window assembly includes a support system with an upper horizontal member, a lower horizontal member, and a pair of spaced apart vertical members, which interconnect the upper horizontal member and the lower horizontal member to define a central opening. The fixed panes adhesively mount to the upper and lower horizontal members. The vertical members have exposed exterior surfaces that are preferably generally flush with the exterior surface of the fixed panes.