(FORTUNE Small Business) – Kevin Russell wants to put me in a jet. Not just any jet. But a jet that meets my traveling needs. "Once you start flying privately, Jeff, you never go back to flying commercially," asserts Russell, who is seated on a private jet across the aisle from me in a leather-covered easy chair that cost $40,000 to make. "Every 30 months we redo all of our cabins." I start counting the chairs in the cabin, which seats 13. I'm thinking I should have taken the time to wipe my feet before climbing aboard.

Russell is a senior vice president at NetJets, the pioneering fractional-jet-ownership company based in Columbus, Ohio. The concept was developed in 1986 by NetJets founder Richard Santulli, a former Goldman Sachs executive who figured there was a market for people who wanted to share ownership of a private jet without shelling out the millions of dollars it would cost to own an entire aircraft themselves.

The company currently manages a 421-jet fleet. By the end of this year, Russell figures that number will be closer to 550, an increase fueled in part by the growing interest in fractional ownership since Sept. 11. (You can't read anything these days without running into one ad or another pushing the joys of fractional ownership. I'm here to see what all the fuss is about.) The big question, of course, is this: Is it worth it? Unless you and your colleagues spend a lot of time in the air, going to mostly remote locations, the answer is probably not. But to be fair, you have to do the math. And if money is no object, by all means sign up!

My experience as a jet owner, or a prospective one, starts on the aforementioned jet, a $35 million Gulfstream IV-SP, whose cabin features a convection oven, a microwave, a polished-wood interior, and a lovely divan with brocade-covered throw pillows. There are eight small monitors and two 14-inch monitors, on which you can watch two movies simultaneously.

Before boarding, I'd already learned one of the advantages of fractional ownership. I'd gotten directions to the regional airport in Bedford, Mass., the prior evening, but it wasn't until I was nearing the border of Rhode Island at 7 A.M. that it struck me that perhaps I might be going the wrong way. My flight was scheduled to leave at 7:45. I called the air terminal office to say I would probably miss the flight. My pilot, Captain Halverson, got on the phone and told me to relax. They weren't going anywhere without me.

Once we're airborne, the ride is smooth; with a cruising altitude above 40,000 feet, the jet travels higher than most commercial traffic. The captain invited me to ride in the jump seat behind him, something I would not recommend to those who would rather not see how high up 40,000 or so feet is. On the plus side, it's a less claustrophobic flight when you're not squeezed between two guys whose idea of good grooming is dousing themselves in Old Spice. Or maybe there's something soothing about knowing the pilots are going to do everything they can to save those $40,000 chairs. I'm in flight and relaxed--or as relaxed as I get under such conditions.

With fractional ownership, you pay only for the hours between the time the wheels go up and touch down. With charter services, by contrast, you don't always know what kind of aircraft you're going to get, and you will typically be charged extra if a jet needs to be flown in from somewhere else. Once you buy your share, just call NetJet four hours ahead and tell the passenger-service team where you want to go and when. Of course, you pay for all those privileges. "It's a quality-of-life decision," Russell tells me. Translation: Ladies and gentlemen, get out your checkbooks.

The general rule of thumb in the fractional industry is that unless you plan to fly more than 50 hours a year, commercial or charter flights might be a better option. In a fractional-ownership deal, you can buy as little as one-sixteenth of a share (committing you to 50 hours a year) to as much as one-half a share (committing you to 400 hours). There are three costs associated with buying fractional ownership: the acquisition cost, the monthly management fee, and the occupied hourly fee.

The acquisition cost is a one-time deal. It's what buys you your piece of the jet. For the Gulfstream IV-SP that we're flying on now, for example, a one-sixteenth share will set me back $2,040,250 for the acquisition cost. The monthly management fee is $14,020. And it'll run me $3,045 per hour to keep the plane in the air.

Let's review: If I pay outright for my share and my 50 hours, we're looking at $2,360,740 in first-year costs. In subsequent years the annual charge to fly the same number of hours will be roughly $320,490. So, forgetting the $2,040,250 acquisition cost for the moment (which for those of us who are in the market to buy a jet is a simpler exercise than for those of us who balk, say, at the idea of having to shell out $22 for overnight parking at Boston's Logan Airport), I'm looking at $6,409.80 for each hour I fly alone in my share of my private jet. But if I fill the jet with 13 people each time, that number drops to $493.06 per person, which doesn't seem like a bad deal, considering NetJets can take me to more than 3,500 regional airports in addition to the country's 500 or so commercial airports.

But then there's that pesky acquisition cost of $2,040,250. If you figure that into your costs over a five-year period, which is how long the contract with NetJets lasts (although it can be rolled over until the jet is taken out of service or you opt for a different model), the hourly rate bumps up to $14,570.80 per hour if I'm alone and $1,120.83 if I fill the plane with 13 people. And though Kevin is too polite to say it, he isn't sure I have that many friends or family who are itching to go anywhere with me.

But remember that Kevin Russell, who's been telling me all this, wants to put me in a jet that's right for me. Kevin thinks I might be happier looking at one of the smaller jets on the left-hand side of the glossy-paper fleet triptych he uses to show me the options.

Rather than select the pricey Gulfstream, I could go with a one-sixteenth share of the Citation V Ultra, the entry-level option. That would set me back a mere $375,000 in acquisition costs, $5,420 in monthly management fees, and $1,343 per hour in the sky. Of course, it can seat only seven.

Hold on. I'm caught up in the moment. I'm basking in luxury and find myself actually thinking that I might buy in to one of these things. Be forewarned when you go shopping for your jet (and to hear Russell talk, you will indeed consider shopping); be prepared for thoughts to overtake you ranging from "If I moved a few thousand over from petty cash and toned down the annual picnic, this baby would be more than affordable," to "Now, if we pick up Jimmy at camp in Indiana, swing over to Ithaca to grab Suzie right after graduation, and then head down to Miami to swoop up Nana after her bridge game, we could make it to Capistrano in time for the swallows." By the end of the test ride, you'll be thinking that owning a share in this jet makes as much sense as leasing a Lexus so that you can drive in luxury. Think again.

No matter how you work the numbers, buying into fractional ownership is going to be more expensive than taking commercial flights. Before the scent of fresh-baked macadamia-nut cookies wafts over you as you sink into your fine leather armchair, get this through your head: You are not going to "make the numbers work" when you try to financially justify opting in.

Oh, sure, the luxury, convenience, and comfort will get to you. What's not to like about being pampered with hot washcloths and having your own personal flight attendant? But then, if you decided to buy something every time you gave into these enticements, you'd have bought that hideaway in Banff, hired that full-time masseuse, or leased that fleet of Hummers because you want your staff to be a commanding presence on the road.

It's going to be mighty hard to justify buying a share in one of these jets, whether it's from NetJets or any of the number of companies that have copied its pricing and ownership model (see chart). But here are some methods of justification to consider: One is that the convenience of being able to fly anywhere on short notice may be worth the additional cost. If you're a retailer who has to frequently meet with vendors at the stores in your far-flung chain, it could end up a bargain. Another is if the additional security of knowing precisely whom you're flying with is worth the extra bucks. Still another is if you place a premium value on that extra legroom you've been carping about for decades. A final one is if a private jet will add nicely to the aura of wealth you're keen on presenting.

There is, of course, another reason to buy yourself a share, namely, the company you'd keep. Warren Buffett owns the business, and who doesn't want to rub elbows with one of the wealthiest men in the world--even if he dresses exactly like your high school driver's ed instructor?

Given all the variables, if you decide that fractional ownership makes sense for you--and using the reasons above, you conceivably could--Kevin Russell doesn't want you to go for the first jet that catches your fancy, because he wants to put you in the jet that's right for you. Once you find it, would you mind swinging by Bedford to give me a lift?

Jeffrey L. Seglin (jseglin@post.harvard.edu) teaches at Emerson College in Boston.