"Standard's actions and secret[14] transport deals helped its kerosene price to drop from 58 to 26 cents from 1865 to 1870. Competitors disliked the company's business practices, but consumers liked the lower prices." - Wikipedia

Not a malevolent monopoly in any sense. Once they had gained the dominant industry position, sure, they could have price gouged for a short time, but without government protection, my claim is that they would have lost their position. They knew that, so they didn't.