Oil=energy. If the supplies dwindle and costs rise, it will make alternative sources more attractive and economically feasible. We have been using oil for energy for less than 150 years. There is nothing to say that in the year 2100, we will still be wedded to its use.
In 1900, we were still wedded to horsepower. The thought of most American families owning a luxury like a car was inconceivable. Let alone, 2 and 3 car 'families'.
Who knows where we'll be in 2100?