Abstract: Methods and apparatus for enhanced recovery of subterranean deposits employ a heated fluid driven into the subterranean formation. A heating fluid is heated at the surface of the earth remote from the subterranean formation to a heated state providing a temperature sufficient for a conversion of a liquid to a vapor phase at the subterranean formation by a transfer of heat from the heating fluid to that liquid. The heating fluid is circulated in a closed circuit extending for the heating fluid at the heated state to the subterranean formation and then back to the earth surface for repeated reheating at that surface to the heated state and for circulation of the heating fluid at said heated state to the subterranean formation.