A reactor includes a reactor vessel and one or more reaction tubes A number of tube sections of the one or more reaction tubes in each case run between a first region and a second region in the reactor vessel. For the electrical heating of the tube sections, the tube sections in the first region can be electrically connected to (a) current connection(s) of a current source. In the first region, current feed arrangements are provided; in each case one or in each case one group of the tube sections are electrically connected, and each comprise (a) contact passage(s) that in each case adjoin(s) at least one of the tube sections in the first region. A wall of the contact passages in each case is connected to a current feed element that has a rod-shaped section that runs at a wall passage through a wall of the reactor vessel.