Question

What did John D. Rockefeller do to establish Standard Oil as a monopoly?

Answer 1

by buying out smaller companies and working with the railroad companies to put his rivals at a disadvantage. Also at one pint he owned 90% of the oil industry in the united states.
Hope this helped :)

Answer 2

bought stock options.

Step-by-step explanation:

Standard Oil benefited from the purchase of stock options and became the world's largest oil company. Numerous competitors were absorbed by Standard Oil for the purchase of stock options. As a result, production increased and prices became competitive. The oil industry flourishes and Standard Oil becomes the leader of this new market, becoming a monopoly.