The flooding capacity of a fractionation tray (2) is increased by the addition of at least one layer of low surface area grids (3) above the inlet to the downcomers (6,12) located on the tray (2). The grids (3) extend upward for a distance equal to one to four times the depth of the downcomers. The grids may rest upon the top edge of the downcomers or on the tray decking between the top portions of the downcomer sidewalls.