And that's significant. Because according to researchers like Thomas Lys, a professor at the Kellogg School of Management at Northwestern University, cash deals are typically more successful than stock deals, when viewed over the short- or medium-term.

"The facts are that typically stock deals are bad and cash deals are good," Lys says. "And by good and bad, I mean upon announcement of the deal there is a significant negative market reaction to the stock deals and a positive reaction to the cash deals."

That divergence continues five years down the road, according to Lys, with the stock prices of the acquiring companies in stock deals deteriorating further over time and the stock prices of the acquirers in cash deals appreciating further.

Why cash deals do better than stock deals is a matter of huge debate among both academics and practitioners. It's also something of a minor miracle because, all other things being equal, stock deals enjoy a distinct advantage over cash deals due to U.S. tax policy.

"If you do a stock deal, you have an opportunity of doing a tax-free deal,' says Lys. "If you do cash, you have no option. It's always taxable. So the stock deals are the ones that potentially could have very large tax benefits to the parties involved. Cash deals offer no such opportunities."

So what is it about cash deals that allow them to overcome this hurdle coming out of the gate and outperform stock deals?

One theory is that when a company uses stock to acquire another company, the inference that investors draw is that the managers believe their stock is overvalued and are acting to take advantage by using this inflated currency -- rather than cold hard cash -- as consideration. So investors do the rational thing themselves and dump the acquiring company's stock.

Steven Kaplan, an M&A expert at the University of Chicago Graduate School of Business, says some of the edge cash deals enjoy, on the other hand, may stem from the fact that they undergo an extra level of examination.

Most cash deals, after all, use borrowed money and so bankers cast a critical eye on the acquiring company's claims about synergies, cost savings and valuation before they pony up.

"Maybe that extra layer of scrutiny adds more discipline and a lot of bad cash deals simply never get off the ground," says Kaplan.

But Cary Kochman, the Chicago-based co-head of U.S. M&A at UBS AG, says he's skeptical of cash-versus-stock generalizations. "These things are highly time specific, fact specific and culture specific," he says.

He thinks that if there's any truth to the generalizations, it probably reflects the fact that all-stock consideration is more likely to occur in bigger deals, where integration complications can weigh on their short- and medium-term stock performance.

"One of the things that is very true is that if you look at large and in particular the largest transactions, they tend to predominately be stock transactions," Kochman says.

"So if you look at the Top 10 global deals of all time, nine of 10 would be completely stock transactions and one of them would be a mix of cash and stock. And in fact if you look at the largest deal this year - the Gillette-P&G transaction - it was entirely stock."

Which is a reminder of something else comforting about the deal-making we're seeing this year. While 2005 is on track to be the best year since 2000 for deal-makers, the fact that P&G's $57 billion buyout is hands-down the biggest transaction is a reminder that 2005 is not a repeat of 2000, when America Online bought Time Warner for $181.6 billion in an all-stock deal what was then - and remains today - the biggest such transaction in history.

And one of the worst deals in history, to boot.

Of course, that wasn't how it was greeted by analysts at the time. At the time, it was billed as a mega deal, a combination of old media and new media, a deal that would unseat Microsoft. It was, in fact, billed as just about everything except what it turned out to be: proof that corporate America was in the midst of a buyout bubble that would soon pop.

Fortunately, that kind of heavy breathing among the analysts has been noticeably absent as this year's deals have been unveiled. And that may provide the best reason of all to believe that the current wave of deals hasn't reached the unsustainable point of bubblehood.

At least not yet.