Which business practice did Rockefeller repeatedly use that helped him succeed in building his oil monopoly?
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.
With every purchase of a refinery, Rockefeller would add new products to his business.
In all his businesses, Rockefeller made sure that he controlled all aspects of production.