People investing in futures do this every day, and some of them are most certainly credible. Southwest Airlines, e.g., seems to be pretty good at saving a buck with aviation gas futures (though that is a step removed from crude oil).
If it were possible to do significantly better than blind luck in speculation about future prices then there'd be nobody around to take the other side of the contract.
The reason why trades occur at all is that not everyone is a pure trader. Hedgers (e.g. Southwest) trade futures to reduce business risk rather than to make money. They tend to make a net loss on trading but earn back a greater amount of money via their core business.
Also: Southwest buys fuel futures to hedge its exposure, which is different from speculation. People hedge because they don't know what the price will do, and want to be OK regardless of price movements.