One mistake the railroad companies probably made in the 20th century was to think of themselves as railroads rather than transportation companies. Had they more foresight, they might have gotten into the airline industry and the auto industry, and been major players in shaping the transportation world we see now. Instead, however, they ceded autos to Detroit and airlines to Seattle, and eventually lost their chokehold on transportation.
Perhaps the oil companies have learned something from the railroads. Any smart oil company should realize that its primary business has shifted to energy in whatever form it takes, not just oil. BP changed its tagline from "British Petroleum" to "Beyond Petroleum." Maybe Exxon Mobil is realizing that it's time to think past oil, too.