A process for recovering hydrocarbons from an in situ formation. The process includes the steps of injecting solvent though an injection well into an underground extraction chamber having a hydrocarbon extraction interface, warming the hydrocarbons at the extraction interface to cause the hydrocarbons to flow downwardly by gravity drainage. Barrier gases naturally emerge in the chamber as a result of the extraction process and are removed from the extraction interface to improve heat transfer from said solvent to said interface. The last step is to recover liquids such as hydrocarbons and water through a production well. The invention provides a separate flow path to remove hydrocarbon gases from the chamber at a preferred location. The preferred location is near the top of the chamber where the accumulated barrier gases help to limit the heat loss and can also provide a barrier to help maintain chamber integrity and confinement.