The invention relates to a reservoir tank for a reducing agent (1), in particular an aqueous urea solution for the after-treatment of exhaust gas from a combustion engine, comprising an outer container (2) and a pot-shaped inner container (3) which limits a partial volume (4) of the volume (5) of the outer container (2), a heating element (6) which is set in the inner container (3) and an extraction device (7) for extracting the reducing agent (1). According to the invention, the pot-shaped inner container (3) is surrounded in the floor region by an insulated collar (8) comprising a first limb (9) led to the outer circumferential surface (11) of the inner container (3) and a second limb (10) contacting the floor surface (12) of the outer container (2), such that the insulated collar (8) limits an additional partial volume (13) of the volume (5) of the outer container (2).
