A new strategy for heavy oil recovery is identified for layered reservoirs, where hydraulic restrictions or barriers to vertical flow separate adjacent oil-saturated strata. Passive heat conduction from a thermal operation in one layer is used to preheat bitumen in the adjacent strata. Once preheated, the oil properties within the adjacent strata are favourably conditioned to either primary production or the effective in-situ application of solvents. This strategy permits greater thermal efficiency for heat either applied or generated within the reservoir, producing a higher recovery and access to otherwise uneconomic pay intervals. A key insight in the passive heating assisted recovery method (PHARM) process is that the reservoir is preheated without the introduction of a secondary working fluid for heat transfer. To the exploitation of the secondary zone, this forms something of an ideal situation. In thermal, solvent-assisted or pure solvent applications, a means of heating heavy oils is essential to an economically effective process. Commonly, heat is introduced to the formation directly by means of a preheated working fluid. Working fluids, such as steam or condensing solvents, carry related costs, design restrictions and potential productivity impairment limitations with their application. If heat otherwise lost from an offsetting thermal process, or in-situ heat generated from waste fuel in offsetting strata, can be harnessed, the desired bitumen heating can be achieved independent to the introduction of an in-situ working fluid for heat transfer. Limitations inherent to the cycling of a working fluid for heat transfer are consequently overcome. As an example, the PHARM strategy can be applied within the bitumen-saturated Grosmont formation, per the geological stratification within Laricina's Saleski project. Here, the Upper Grosmont C and D strata are separated by a regional marlstone, which, in areas forming a vertical hydraulic flow restriction, does not constitute a thermal barrier. Thermal processes in either layer will passively heat the adjacent strata by conduction. The preheated bitumen layer, rather than presenting a process heat loss, can now be more effectively exploited. The inherent advantage permits incremental bitumen volumes to be accessed at a markedly reduced CSOR equivalent. For a steam assisted gravity drainage (SAGD) process, a generic example provided illustrates an overall CSOR reduction from 3.2-2.5 for primary drainage, with potential system CSOR reductions below two with the application of solvents. Solvents further permit access to a significantly lower-permeability reservoir where the host rock below 100 md may be resourced.