FIELD: mining. ! SUBSTANCE: invention relates to the field of mining and can be used to develop deposits of hydrocarbon fluids, particularly in the production of high-viscosity oil and natural bitumen with a high gas factor. In the method for developing a deposit of bituminous oil from a horizontal well, which includes exploration of a deposit to identify areas with gas caps, the construction of a horizontal well under the gas cap with the opening of the reservoir, drilling appraisal wells above the horizontal well with the opening of the gas cap, descent into the horizontal well tubing, cyclic feeding of water vapor along the tubing with expectation of thermocapillary impregnation and selection of well production, preliminary determine the presence of dome-shaped uplifts in which gas caps are located, horizontal wells are built under these uplifts, a couple of appraisal wells drilled along the axis of the horizontal well beyond its limits at a distance that allows to isolate the space of the gas cap above the horizontal well, before injecting steam into the horizontal well, fillers are pumped into the evaluation wells to isolate the space of the gas cap above the horizontal well. ! EFFECT: exclusion of breakthrough of the coolant into gas caps, reduction of energy and material costs for heating up the reservoir. ! 1 cl, 2 dwg, 1 ex