Which company was a monopoly during the Gilded Age?

Carnegie steel was one of the main monopoly holders of the gilded age. Throuthout its operation, Carnegie steel constantly bought out all the promoising small business in the steel industry to prevent them from becoming their competior. This way, they became the sole producer in steel industry during that period

The appropriate response is Carnegie steel. It was a steel delivering organization basically made by Andrew Carnegie and a few close partners, to oversee organizations at steel processes in the Pittsburgh, Pennsylvania range in the late nineteenth century.