Deeply-buried and high-bitumen-content crude oil is one of the most important energy resources. Currently, Steam- and Solvent-Assisted Gravity Drainage (SSAGD) is an attractive, but a high-cost and high-carbon-emitting method for exploiting this type of resource. In order to evaluate the greenhouse gas (GHG) emission and economic performance of SSAGD, it is critical to predict the energy efficiency and solvent retention in the steam chamber. However, the fluid property profiles inside the steam chamber, which are directly related to energy efficiency and solvent retention, have been rarely investigated. In this work, a semi-analytical model is developed for examining the property distributions within the steam chamber, considering the complex interaction of energy and mass transfer along with the effects of phase behavior. Subsequently, the solvent retention and energy-utilization/-saving efficiency are carefully analyzed on the basis of the calculated property profiles inside the steam chamber. The proposed method is mostly based on analytical relationships and is free from certain simplifications that may affect the calculations of energy efficiency and solvent retention in the SSAGD process. Furthermore, the optimal solvent type and injection pressure obtained with the model can reduce the GHG emission and improve the economic benefits of future SSAGD projects.