A method is provided for applying a thermal process to a lower zone underlying an overlying hydrocarbon zone with thermal energy from the thermal process mobilizing oil in the overlying zone. The lower zone itself could be a hydrocarbon zone undergoing thermal EOR. Further, one can economically apply a thermal EOR process to an oil formation of low mobility and having an underlying zone such as a basal water zone. Introduction gas and steam, the gas having a higher density than the steam, into the underlying zone displaces the basal water and creates an insulating layer of gas between the steam and the basal water maximizing heat transfer upwardly and mobilizing viscous oil greatly reducing the heat loss to the basal water, economically enhancing production from thin oil bearing zones with underlying basal water which are not otherwise economic by other known EOR processes.