Steam-assisted gravity drainage (SAGD) has become the most popular in situ method for recovering bitumen in Alberta, but it remains an operationally challenging process. A particular challenge is the maintenance of a liquid pool, or steam trap, around the production well to prevent the influx of live steam, which reduces energy efficiency and increases the risk of eroding production equipment. In this thesis, an analytical model called a gravity inflow performance relationship (GIPR) is formulated to describe the flow through the steam trap. The model enables efficient prediction of the liquid level above the production well, providing a valuable tool for optimizing SAGD well designs and control strategies. The GIPR is verified against simulations using a higher-order numerical model. Then, the GIPR is coupled to a wellbore hydraulics model to study the uniformity and stability of the liquid-vapour interface along the length of a SAGD well pair. Three case studies are conducted with the coupled model, each investigating a different operational challenge, and each providing fundamental insight into the mechanics of steam trap control.