The volume of heavy oil and bitumen in the oil-sands deposits in western Canada is similar to that of conventional crude oil in the Middle East. This resource is immense but is difficult and energy intensive to extract because the viscosity of the oil is high, typically greater than 100,000 to 1,000,000+ cp at original reservoir conditions. Current commercial thermal-recovery processes used include steam-assisted gravity drainage (SAGD) and cyclic steam stimulation (CSS). These methods are energy intensive, emit significant amounts of CO, into the atmosphere, and use large volumes of water to recover the oil. In this work, the focus is on SAGD processes. It has been demonstrated that operating strategy can be altered to improve SAGD performance, but it is not clear how well configuration can be changed to improve recovery, energy intensity, thermal efficiency, water use, and flue-gas emissions. This paper examines the impact of position and geometry of steam injectors on the performance of steam-based gravity-drainage processes in a heterogeneous reservoir. Different injection-well configurations including single horizontal (typical SAGD), offset SAGD, and vertical/horizontal well combinations have been evaluated by using a detailed, 3D, geostatistically populated, large-scale thermal reservoir-simulation model derived from core-data examinations of the Dover pilot site. The research reveals how injection-well configuration impacts energy delivery to the reservoir, how it affects thermal efficiency, and how it changes the evolution of the steam-conformance zone and oil-flow dynamics in the reservoir. The results suggest that several vertical injectors have the potential to deliver steam more efficiently than a single horizontal injector.