What made standard oil a horizontal integration monopoly?
it controlled all aspects of oil production.
it owned ninety percent of us oil refineries.
it formed a trust.
it operated all across the united states.

I believe the answer is: It owned ninety percent of US oil refineries.

At the peak of its power, Standard oil managed to buy out almost all of its competitors and provide oil consumers with barely any options in choosing their oil products. They do this in order to gain leverage to control oil prices since there was no competition that can threaten their consumer base.

B) It owned ninety percent of US oil refineries

i'm free to do it

explanation: