Recovering hydrocarbons from tar sand or heavy oil reservoirs

Method of recovering fluids from an underground tar sand reservoir or heavy oil reservoir comprising (a) drilling and completing a first pair of wells and a second pair of wells, each pair comprising an injection well terminating in the reservoir and a production well terminating in the reservoir below the injection well; (b) circulating steam through the injection wells and performing alternate steam injection and fluid production through the production wells; and (c) injecting steam through the injection wells while producing fluids through the production wells, wherein the injection pressure of the injection well of the first pair of wells is greater than the injection pressure of the injection well of the second pair of wells.