Thanks for your reply, Sigma.
I generically agree with your point, but I think there is room to put a reasonable range on this, particularly for the folks who have played this game for much longer than the many of us noobs.
I would surmise from your statement that we can reasonably expect a top end around $1200-1300 (i.e. way way north of $1000). While it could come to that, I think it would have devastating economic effect, such that only the long established players with stacks of cash could ride it out. This result would make for a not so fun game for several players (unless, of course, the Pax demand model would allow the rest of us to jack up the price by about 3x, and the level of demand would remain - that is, it recognizes and adjusts for that level of inflation, and therefore is price insensitive). I've not played enough games to understand how that model behaves.
The pattern in DOM for the past two game years suggests that spikes are unlikely, though no telling if there would be an OPEC 1973 like event programmed. There seems to be a more gradual ebb and flow, possibly around some moving equilibrium point that itself resets at some interval, perhaps quarterly. Volatility around the equilibrium seems consistent, percentage wise. So, I am guessing that a peak could last +/- for a six month period (perhaps only to recede for a quarter to head back up for another six months). Again, this is an observation of part of the DOM game, and part of the Beginners World.
So, I agree it is not specifically knowable, but I think those with experience across multiple games have gained some knowledge about the general behavior of fuel prices and what is a reasonable top end. Perhaps I've guessed it here.