In recent years, substantial progress has been made in the theoretical treatment of,hydrocarbon dissolution in water, near the critical point of water (374 degrees C). At these temperatures, water becomes a solvent for gases including the lower hydrocarbons, and possibly, the higher hydrocarbons. The SAGD process is currently the only viable method for in situ recovery of Canada's, Athabasca oil sands deposit, a deposit of high viscosity oil in unconsolidated sand. Recent studies have sought to understand modifications at lower steam pressures and gas injection. Most recently, the idea of solvent co-injection has been under discussion. In the present paper, the predictive capabilities that have been developed for gas production in the SAGD,process are studied in conjunction with the chemical-kinetics,and mechanisms of solvolytic reactions. The reactions that produce hydrogen sulphide and carbon dioxide, generally referred to by the name "aquathermolysis," are thought to be solvolytic reactions by their nature The results of this work suggests strongly that,the production of the acid gases, hydrogen sulphide, and carbon dioxide suppressed in SAGD operations if a solvent is co-injected. The work has implications for the need for sulphur recovery plants in, SAGD projects that are considered for solvent co-injection. Recently published thermodynamic data have made possible the prediction of individual solvent component production or retention in the steam zone.