Which business practice did Rockefeller repeatedly use that helped him succeed in building his oil monopoly? In all his businesses, Rockefeller made sure that he controlled all aspects of production.
With every purchase of a refinery, Rockefeller would add new products to his business.
In all his businesses, Rockefeller made a profit and used it to expand or buy other businesses.
With every business Rockefeller bought, he would learn about it, sell it at a profit, and buy another business.