veggie oil weight does matter
 

today i took the Chevy Colorado to go get a hundred plus gallons of vegetable oil.. the best i was able to pull off was 33.5 MPG usually i can break 35 mpg for a round trip.. weight surly matters .. I had the two 55 gallon barrels tucked up next to the cab witch should have helped areo-dynamically.. the barrels weigh about 300 pounds each i was hauling about 600 lbs of raw oil and my MPG surly was hit by the added weight.

What are you hauling Veggie oil for?

In town, I'll bet it (weight) matters a good bit
On the highway I'd say that the tires would be the primary determining factor . . .

So you are estimating 6 lbs/ gallon? I was thinking it was more like 7~8 lbs/ gallon. Maybe I can haul 100+ gallons with the golf after all.

Water weighs 8.33 pounds per gallon, and most of the things I've read use that same 8 pounds per gallon weight.

I think the OP had 600# of oil in two 55 gallon containers, but they weren't full of 55 gallons each (that would have been 440 pounds each, or 880 total).