Abstract: A device for a magnetic treatment of a hydrocarbon-containing fluid, which device has a pipe for the fluid to flow through and six magnets, which form three pairs located one after the other, the magnetic fields of which penetrate the interior of the pipe. The magnets are essentially cylindrical and are located outside the pipe, the two magnets of one pair being located in alignment with one another on opposite sides of the pipe wall and each pointing with one of its face ends to the pipe, and each magnet having a line pattern of alternating magnetic polarization, which is oriented perpendicular to the flow direction of the fluid.