Read the following passage, then answer the question. John Rockefeller might get his oil cheaper now and then, they said, but he could not do it often. He might make close contracts for which they had neither the patience nor the stomach. He might have an unusual mechanical and practical genius in his partner. But these things could not explain all. They believed they bought, on the whole, almost as cheaply as he, and they knew they made as good oil and with as great, or nearly as great, economy. He could sell at no better price than they. Where was his advantage