A device for the in-situ extraction of a hydrocarbon-containing substance, while reducing the viscosity thereof, from an underground deposit, has at least one injection pipeline extending in the deposit and at least one production pipeline leading out of the deposit, which together form a so-called well pair. The injection and production pipelines each have a starting region extending above ground in some areas, and an active region connecting to the starting region inside the deposit. With the method, during a heating phase hot steam is applied to the injection and production pipelines, while during a production phase hot steam is applied only to the injection pipeline. Furthermore, the active region of the injection pipeline is additionally configured as an induction heater regarding the surrounding area in the deposit. In the associated device, for example, the well pair formed by the injection pipeline and production pipeline can be configured as electrodes.