hydrocarbons is established thereby reducing the viscosity of the hydrocarbons the heat of condensation of the solvent is additive to the heat given up by the condensing steam and this helps heat the next layer or zone of hydrocarbons 10 the line 48 in fig3 defines the boundary between the mixing zone 47 and the underlying layer of heavy hydrocarbons in the formation 10 in the mixing zone 47 the solvent goes into solution with the hydrocarbons resulting in a mixture of solvent and hydrocarbons of reduced viscosity which flows under the force of gravity as indicated by the arrows 50 toward the production well 30 by trial and error type calculation it may be found that the process described herein will be in equilibrium when one part solvent has gone into solution with two parts of the viscous hydrocarbons at this concentration the resulting liquid hydrocarbon solution would have a viscosity of 3 43 cp comparing this viscosity to the 90 cp viscosity of the undiluted viscous hydrocarbons at the same temperature it is seen that the viscosity has been reduced by a factor of 90 3 43 or 26 2 times more than could have been achieved with steam alone accordingly the flow rate of the solvent hydrocarbon solution through the formation 10 will be 26.