The prices for oil product (kerosene at the time) went down from 60 or so cents in 1860s to just around 7 cents a gallon by late 1890s.
Why it did not go to 3 cents a gallon? Because Rockefeller colluded with railroad companies and had secret arrangements to get bulk discount for himself and shafted his competitors. Monopolies are not always the result of a company doing everything "right". It is always the result of companies carving up the market using secret deals, cartels, trusts. They maintain their monopoly by destroying the small upstart competitors who had better ideas, better way of doing things, which will bring greater benefit to the society.
In the early days of personal computers, the technology moved so fast the laws and the government were playing catch up. It was, in a sense, closer to utter free markets. Microsoft & Intel emerged as the winners and maintained a near monopoly and a stranglehold on the market. All the things they did that is still fresh in the minds of older Slashdotters, the oil barons and the railroad tycoons did back then, in a much harsher way. That is how Korean and Japanese industrial "houses" work to this day. That is how garment factories are run to this day in Bangladesh and Phillipines.
It is fair Rockefeller was hounded in his old age, forced to flee in a rickety car like a fugitive. He drove so many worthy better oil men to madness and suicide with his secret deals and cartel building. If you are a white person from the current Rust-Belt of USA, it is very much possible one of your ancestors was shafted by this guy, cheated out of a fair price for the oilfield or forced to go bankrupt if he was in oil/railroad business.
You are just a religious fanatic worshiping some ideal "free" market and you will dismiss all the holes as "not really free" market. You are as bad as people who believe communism will work.