The continuation of mass travel over long distances, is inconceivable if the world really runs short of energy. Thus, looking at the year 2000 we have two alternatives:
either: fuel will be strictly rationed and reserved for essential purposes, which certainly would not include long-distance mass-travel,
or: fuel will continue to be freely available to the airlines at some price.
In the first scenario, there is no future for civil aviation as we know it and the aerospace industries must turn to new fields of endeavour.
In the second scenario, we have to answer the question: ‘what fuel at what price?'. This has to be answered because, if the price were to rise sufficiently, then the result would be similar to that of the first scenario as the present travelling public could no longer afford to buy airline tickets.