Hard to say. I suspect airline travel will become unaffordable for ordinary people long before that. Military aircraft, OTOH, might be around for quite some time.

Ah, you raise a VERY interesting question:  The time-frame issue!  Will the demise of mass air-travel take place within something more like five years, or something more like fifty??  Any thoughts, anyone?

[A working definition of "demise of mass air-travel" might be when the point is reached when only the upper-classes can afford to fly on any sort of regular basis; and when those of lesser means are only able to do so at tremendous cost under the most extraordinary of circumstances.]

Absolutely on target. Some retired geologists complain about economists, but all those anticipating the eminent demise of globalism should do some quick math. The cost of fuel is maybe 20% of air line costs, so doubling fuel increases total costs maybe 20%, and increases the overall trip cost a much smaller amount. US and other airlines are having their biggest problems with fierce competition from low cost carriers, usefully lowering our travel costs but driving older airlines with high labor costs into bankruptcy.  

Regarding business air travel, current US ticket costs are dramatically less (many US round trips were over $1500!) than they were a few years ago on account of competition from Southwest and Jetblue, even though fuel costs have tripled. As an aside, if we turned to a single state airline, costs would rise and service would decline, probably sharply in both cases. (Talk about ignoring the benefits of deregulation.)

As noted, if we all have less disposable income on account of higher fuel costs, we will do without some things, and vacations may be one of these, but this is a second order effect.

Shipping costs are for most US imports a very small portion of the cost, in some cases microscopic, so will be very little affected by rising fuel costs. The situation is a little worse for grain exports, but fuel costs are not likely to outweigh the US inherent advantages any time soon.

The big savings to come will be where fuel costs are a substantial portion of the activity AND where they can be substantially reduced, namely commuting. Prius type vehicles combined with four-person car pools would cut commuting fuel consumption around 90%, with additional savings from reduced stop and go and less road building. This change, plus more work from home, will come long before 'the end of suburbia.'

I would not be so hasty with the conslusions from this arithmetics.

Even now most airlines operate on the edge of covering their costs. Why? Because of the enormous fixed costs that must be covered by large volume of travel (airport time slots, planes amortisation and maintainance etc.). In 2004 for the US carriers fuel costs were 15% of the operating costs (at 45$ per barrel). At 90$ per barrel they'd have to raise prices with 15% which is quite significant. They will lose flights, passengers etc., while facing the same fixed costs. Eventually they will have to rise prices again and again while scaling back or simply going out of business.

Put another way if you have the same plane for 100 passengers at 600$ per barel the price for fuel will be 1500 euro and the ticket will be 2000 euro. But the plane will be just 20% full so the ticket will have to be 10000 euro to cover costs. If alternatevly, they cut flights five-fold the price of fuel will be again 1500euro and the ticket will be 4000euro (because of the 5 times higher fixed costs). So they'd have to cut flights again and again...

It is the large middle and low class price-sensitive segment that keeps air companies afloat. If it is gone - so is the air travel. If price gets in the range of 200$ per barrel just forget about air travel.

Teemu has quite right. Besides the oil is not ending now or after the Peak Oil. Read Hubbert and others - oil will not end, the supply will only diminish and quite slowly at that. After 50 years there will be half as much oil as today.

Flying is a relatively effective means of transport so it will not be the first one to stop. But it will decrease, may be back there, where it was in the '50s or '60s.

The world had global trade already in the 16th century. Sailing ships will do if necessary. We should expect the trade volumes to go down, but not to cease altogether. Overly dramatic, unrealistic scenarios will not help. Remember, you all had a peak oil experience in 2000-2002. Anybody noticed a petrocollapse? Yes, the real one will probably be more visible and the supply drop may be more discernible, but the oil will not end suddenly and life change overnight.

Well, your calculations might get worse as time goes on.  As you said when price goes up, fewer people want to travel, but some still do.  But if the airlines only have a 50 person plane, and only 10 people want to travel, well not only is a 50 passenger plane less fuel efficient per passenger seat than a 300 passenger plane, but now it's 1/5 as efficient because of the smaller number of people.  In short, costs per trip will go up faster than one would think.

What ends up happening then, is that all of the carriers who run trips to the smaller air ports have to either cut the freqency down severly, or end up just cancelling the route (if a plane only comes in to Madison, WI once every three weeks, most people will say ef it, I'll drive to Chicago and take a plane from there).  And we end up with only the highest traveled routes being supported.  The simple fact of having to drive hours or a day+ to get to the nearest serviced air port might further cut down into the airlines passenger count, which makes fewer flights possible.  

Eventually, costs per ticket create enough demand destruction that the airlines declare it's just not worth operating anymore.  And then that's the end of air travel.  There will still be privately (corporate or personal) owned planes, and military planes in the sky.  But no commercial planes.

Of course, with many (most?) airlines operating at a loss, and the governments continually willing to bale them out, we're not on that route yet.  But if the government eventually regulates (re-regulates?) that every commercial flight must at least cover costs or else the air line is inelligible for bankruptcy protection or a bail out, well that will be the death blow to the airlines and it will all be just a matter of time.  But then again, this is all just a guess, but it seems feasible in my mind.