Don Pittis, senior producer of CBC News Business. The excitement over the merger between Suncor and Petro-Canada thrilled Canadian markets, so often smacked down by waves of bad news.

But someone has to say it.

Mergers and acquisitions among struggling companies are no guarantee of a rosy future. Not in a company. And not in an industry.

In fact, the collective euphoria that hits markets with every big merger is a perfect example of the kind of short-term thinking and long-term amnesia that led us into the current market meltdown.

Now, it may be that this giant Canadian oil merger is a marriage made in heaven. Maybe these two Calgary-based companies are the ideal fit and, together, they will soar to new heights impossible for them to reach individually. However, all but the most forgetful of us should realize that many mergers and acquisitions do not go so well.

There have been plenty of recent reminders. The rush to consolidate European banking, including the battle to gobble up Holland's ABN Amro, is a glaring case in point. Two of the gobblers, the Royal Bank of Scotland and Fortis Bank, effectively collapsed and have been kept standing only by British and Belgian taxpayers.

We needn't go so far from home. Canadian mining giant Teck got severe indigestion after swallowing Fording Coal. CanWest Global's case of post-merger malady may be terminal, as the company flirts with bankruptcy.

Not a new phenomenon

And, before you say it, this is not a simple product of the recent credit crisis and market collapse. There are plenty more examples from the past. Nortel's attempt to grow by acquisition when it was at the top of its game contributed to its eventual downfall. A friend who worked at the company told me at the time that Nortel was swallowing more than it could digest and was losing focus on its central business.

Do you remember Air Canada's takeover of Canadian Airlines in 2000? Do you remember Air Canada going into bankruptcy protection in 2003?

Despite these examples, I should make it clear there is no sign that these two oil giants together, or separately, are or were in danger of going the way of Air Canada or Nortel. The troubles in the oil sector are of a different magnitude, with lots of financial padding.

But with each of those mergers and acquisitions ("M&As," in the business press), there was much celebration and shaking of hands. Share prices rose. Company bosses got bonuses. Outgoing bosses got golden handshakes. It was only later that the problems appeared.

Mergers bring synergy, or so the theory goes

The theory is that the merged company will do better than the companies individually. As in this case, people say that buying business is cheaper than building business. The word "synergy" always pops up. The other words you hear are "savings" and "efficiencies."

Properly defined, synergy describes an almost mystical state where two entities working together create something special just because they come together. Some marriages are like that, perhaps, and teams of artists or scientists. Watson and Crick. Gilbert and Sullivan. Neither one could have done it alone.

In mergers and acquisitions, however, that mystical improvement is harder to put your finger on. It's like the "goodwill" that's often written onto company balance sheets. Hard to find when accountants go looking for it to fill a gap.

More often, synergy is used as a synonym for savings, which is easier to understand.

Once there were two high-price CEOs, but the new company will only have one. Sales departments, accountants, strategists, trucks, equipment — everyplace there is an overlap, one section can be cut and the other add a few extra people to take up the slack. That's the theory.

In fact, the advantages of synergies and savings are often illusory.

But even when there are savings to be made, on the other side of the ledger are costs that go unremarked in the initial euphoria.

It takes time and attention

Merging corporate cultures and making companies work together takes time and management attention. Getting Nortel's acquired companies working together was a project that was never completed. The public spat between pilots and crew at the merged Air Canada created tensions that hurt the bottom line.

There are some potential positives in the Suncor-PetroCan union. In a world of big players, bigness may be an advantage. Many people say the recent flurry of foreign takeovers in the Canadian mining sector would never have happened had the domestic industry consolidated first.

Suncor gets Petro-Canada's retail operation, something it did not have before. But if the market for oil and gas is as free as everyone in the business says, it shouldn't matter much whether you sell your gas to a retailer you own or to some other retailer.

In the long run, the main cost of an acquisition — paying an above-market price for the company being purchased — must be covered by earning money the two companies could never have earned separately.

As with the airlines, taking two troubled companies and putting them together just creates one big troubled company. We know that the world's economy will relaunch at some point, and Canadian resources will once again be in demand. But whether the oilsands will remain a viable business in a carbon-sensitive world is no more assured after a merger than before.

Suncor's poison pill, inherited from Petro-Canada, may help it become a Canadian champion, too big and too difficult for someone else to swallow. And that may be a good thing for the Calgary-based oil business. Also, anyone who owned Petro-Canada shares has seen a benefit.

But history tells us that whether the merger of these two Canadian titans will make their combined business worth more in the long run is no sure thing.

Don Pittis has reported on business for Radio Hong Kong, the BBC and the CBC. He is senior producer of CBC News Business.