No way would they sell a product without some percentage of profit.
Think about it. Walmart has serious buying power. I'll bet they get the producer to sell them product and the producer makes only a few pennies per quart,but once you multiply those pennies by millions of quarts then that keeps the producer happy since he is getting paid,it keeps walmarts prices low because there isn't a vendor on earth that can compete with their volume.
And wal mart gets special jugs that I only see on their shelves. Like the 4.73 litre jug. So they don't have to price match since those jugs seem to be a Walmart exclusive. In fact when oil goes on rollback or on special its never the 5 litre jugs,just te 4.73 litre ones.
So yes Walmart is making a profit,even when they have their rollback sales because the supplier will supply the volume with less profit margin for themselves.