In the last 10 years, substantial progress has been made in the theoretical treatment of gas dissolution in water, near the critical point of water (374 degrees C). An asymptotic behaviour of Henry's law for a variety of gases (the noble gases, methane, ethane, nitrogen, oxygen, carbon dioxide, and hydrogen sulphide) already governs the behaviour of these gases at temperatures above approximately 180 degrees C, well below the critical point. This behaviour has been used to develop a theory of gas production in SAGD, according to which gas production in SAGD largely occurs via dissolution of gas in the steam condensate. Further recent developments in this area of solution thermodynamics have extended the knowledge of this phenomenon to various light hydrocarbons, from butane to dodecane, and the aromatics such as benzene and toluene. In the present paper, data for the distribution coefficients (K-values) of light hydrocarbon solvents in water are presented, and the application for prediction of solvent co-injection is discussed. Optimal choice of solvent composition to maximize solvent returns is possible.