Abstract: At least two fluids separated from one another are mixed by means of pump force via respective suction lines and conveyed into a conveying line by a pump delivery stroke. The fluids are mixed in the pump head of a single oscillating positive displacement pump, the drive of which is controlled in accordance with a proportion of the fluids to be mixed, the suction stroke of the drive is divided over its rotary angle into individual sections during which the fluids are sucked into the pump head one after another, whereupon the fluids which have already been mixed in the pump head are ejected into the conveying line during the subsequent pump delivery stroke. The suction lines of at least two fluids to be mixed are provided with valves and connected to the pump head, the drive controller of which is configured for switching over the valves.