There can certainly be speculation on commodity futures even without inventories changing hands, and that speculation can affect current prices. Nonetheless, I would suggest that, in a large market, the only way speculators as a group can make money is if they work to stabilize rather than destabilize prices. Of course, it is quite possible for some speculators to make a lot of money by enticing suckers to enter the speculative market. In that case, the former group of speculators can make money from the latter.
I wrote that reason because of all the Freepers here like “Curiosity” who swore up and down there couldn’t possibly be oil speculation and kept screaming “where is the excess inventory. You can’t have speculation without a buildup of inventory.” No matter what I said, they wouldn’t listen. Now they are proved wrong, and where are they? Hiding in their hidey-holes so they don’t have to eat crow, that’s where.