How did horizontal integration enable rockefeller to monopolize the u. s oil industry?

Rockefeller was able to monopolize the u. s oil industry through horizontal integration by producing and selling the same product to different markets, capturing the vast majority of the market for that product or service. This led to a monopoly because he integrated enough of the production market into his own company that he could destroy competition. The Rockefeller corporation produced its own tank cars, pipelines, and even it's own wooden barrels.