I understand your point, but I do not think the resource would become so valuable if only one company controlled this resource.

> Although Standard had 90 percent of American refining capacity in 1880, by 1911 that had shrunk to between 60 and 65 percent, due to the expansion in capacity by competitors [1]

Standard Oil did become hugely rich and powerful. It did reach massive marketshare as a result of cutting prices, but I wouldn't call it a natural monopoly. I see a monopoly as having no competitors.

[1](https://en.wikipedia.org/wiki/Standard_Oil#cite_note-47)