A method and system for producing hydrocarbons in situ from an oil shale, fixed bed, hydrocarbon formation disposed below a ground surface. The hydrocarbon formation having an upper A-Groove higher permeability aquifer zone disposed above a R-rated, kerogen rich, lower permeability zone and a lower B-Groove higher permeability aquifer zone disposed below the R-rated zone. The system includes a plurality of injection wells drilled into the formation and spaced apart from a plurality of production wells also drilled into the hydrocarbon formation. A heated thermal-energy carrier fluid is circulated under pressure into the injection wells, circulated under pressure through the A-Groove and B-Groove aquifer zones for mobilizing selected hydrocarbons in the R-rated zone and pumped from the A-Groove and the B-Groove aquifer zones upwardly under pressure through the production wells to the ground surface. Selected hydrocarbons are then removed from the carrier fluid. The carrier fluid can be recirculated back into the injection wells.