Steam Assisted Gravity Drainage (SAGD) is an in situ thermal recovery technique used at Petro-Canada's MacKay River Project. The objective of this study is to develop an analytical well test method that would allow a measure of steam chamber volume and potentially the timing and location of steam chamber coalescence. This well test method would also prove useful in determining an analytical solution for near wellbore characteristics and reservoir boundaries. A pseudo-compositional thermal simulator was used to generate reservoir pressure responses by shutting off an injector at different periods of time and monitoring the pressure fall-off while continuing with production. Confined, unconfined, and coalesced 2-dimensional sink-source well pair models, based upon the geology and drilling pattern at Petro-Canada's MacKay River Project, were used in the study. The effect of the magnitude of the vertical permeability and the vertical to horizontal permeability ratio on the shut-in pressure response was also studied so that this method could be applied to other reservoirs of differing geology. Pressure response type curves were generated and the relationships between pressure drop at the injector, shut-in time, and steam chamber volume were determined. We show that the pressure response type curves are unique for different types of SAGD wells and levels of steam chamber development. This information will aid in determining the timing of operational conversions and determining recovery factors and possibly locations of reservoir boundaries, as well as steam chamber coalescence.