How was rockefeller able to build his monopoly across the oil industry? he found newer and cheaper ways to refine oil, increasing his profits. he confined his business to ohio so he could buy all the refineries there. he bought up oil refineries, cut costs, and reinvested his profits in other refineries. he began to sell kerosene as well as oil, expanding his market.

He bought up oil refineries, cut costs, and reinvested his profits in other refineries. Option C is correct.

Rockefeller was an American oil industry business magnate, industrialist, as well as philanthropist. He is widely regarded to as the wealthiest American of all time, and the richest person in modern history.

Rockefeller's wealth sky rocketed as kerosene and gasoline grew in importance, and he turnt into the richest person in the country, controlling 90% of all oil in the United States at his peak.