Monopolies don't work and they have been a boogey man of American business it would appear. Standard Oil only drove out of business those smaller and more inefficient suppliers. It appears that in the 1880s and 1890s it was actually a bad thing to drive down prices. Discounts weren't viewed in the same light as they are today.
During the 'heyday' of Standard Oil the number of refineries and oil companies increased - as did the market.