I think it's a matter of interpretation. PLUTO certainly didn't revolutionize the supply of petroleum to the Allied beachhead or advance out of Normandy. It just couldn't provide the volume that was required by a fully mechanized cross-Channel invasion. So, in that respect it was a failure. However, I would lump it in with the Mulberry harbors, amphibious and specialized tanks, airborne operations, preparatory bombardments by air and sea, and nearly every other measure applied to the invasion--none of them were unqualified successes but each of them helped make the invasion successful. So, PLUTO didn't solve the Allies' supply problems, but every gallon it did provide was one less that had to be supplied by another source. Since the Allies could afford to spend lavishly on projects that didn't have to succeed, the drawbacks of PLUTO and the other invasion 'flops' weren't too costly. So PLUTO was a qualified success with major drawbacks, in my opinion.