Abstract: Continuous flow membrane separation is accomplished by apparatus adaptable for osmosis, dialysis, and electrodialysis. For electrodialysis to separate from one another, in a single step, multiple differing molecular weight components of fluids, a series of adjoining flow chambers are all separated from one another by semipermeable membranes and at least one of the chambers is separated from each adjoining chamber by a membrane having a molecular weight cutoff different from that of the membrane separating it from the other chamber adjoining it. To insure that neither the crude to be processed nor the desired product comes into contact with an electrode which could be deleterious, there is provided a minimum of four flow chambers adjoining one another in sequence.