Private landowners would sell their rights either directly to Standard Oil, or to companies owned by Standard Oil. If you can point to a deal where Standard Oil bought mineral rights directly from the government in some kind of corrupt deal, I'm all ears.

Or are you arguing that the right to own private property comes from the government? What then, is the proposed alternative? Dispel property rights? Because history indicates this is likely to make the problem of monopolies worse instead of better.

They bought them from landowners, sometimes through nefarious means if you remember your early 20th century literature.