Though Delta and Northwest have asserted that a merger will help them cope with skyrocketing fuel costs, it won't do much to cut their fuel bill.

At best, they can use their greater size to offset fuel costs by trimming in other areas or raising prices. When it comes to fuel, there are no volume discounts. And while a company can hedge to smooth out spikes, it can't fight the long-term tide of rising prices.

There's no getting around it: Buying more fuel at higher prices means spending more money.

"It's a huge expense," said Bradford Hudson, marketing professor in the School of Hospitality Administration at Boston University. "It is uncontrollable."

Still, there is no doubt that the price of fuel is a key reason for the massive, high-stakes merger.

Delta President Ed Bastian said in an interview Wednesday that he doesn't expect the deal to mean lower fuel costs. But the merged companies can manage fuel costs by controlling other parts of the business, he said.

"There is no model out there that is going to be able to withstand a run-up of fuel from $70 to $115 (per barrel of oil) and be able to turn profits consistently," he said. "But we have to find a way to be able to take the scale of the combined entity and get to a point where our combined network can price to where fuel currently is at."

Fuel costs have become an increasingly painful burden: The price of jet fuel has soared from less than 50 cents a gallon in 2001 to more than $3.40 this week. Delta, which last year had revenues of $19 billion, spent nearly $4.7 billion on fuel.

That expense comes despite a drop in recent years in how much jet fuel is being burned.

Use peaked in 2000, slipped the next year as the recession began, dropped dramatically after the 9/11 terror attacks and has never fully recovered.

Because they often fly smaller or more efficient planes, and because demand has been soft, airlines are using less jet fuel than they did a few years ago, according to the U.S. Energy Information Administration.

In January, about 1.5 million barrels of jet fuel were consumed compared to 1.6 million the same month of 2007.

A merger can significantly improve finances — but in other ways, Hudson said. "You merge to save money, by merging administrative offices and headquarters employees and to bust unions — because unions are a serious cost item."

Airlines can also become more selective about the routes they fly.

All told, Delta and Northwest officials estimated that the combination can save them $1 billion in expenses.

But when it comes to fuel, a merger doesn't dramatically change the calculation, Hudson said. "I find it hard to understand how the merger is driven by fuel prices. The airlines were in trouble before oil prices went up."

Airlines are costly to run in the best of times. The industry is capital-intensive, it requires trained and relatively expensive staff. Moreover, flight patterns are so intertwined that weather and equipment glitches in one city can easily ripple across the system to cause delays — and cost money — thousand of miles away.

And trouble is often exposed in a harsh, public and national glare.

Companies have limited pricing power: Several decades after deregulation, head-to-head competition has conditioned fliers to seek the lowest-priced tickets — a search supercharged by the Internet.

Then came rocketing fuel prices.

Both Delta and Northwest have been through bankruptcy, but they are hardly the only ones who have struggled.

"The airline industry has a broken business model," Hudson said. "The problem is that nobody knows what the business model needs to be."

Adding yet another challenging layer is the current economy — where growth is sluggish at best and many economists are now saying that the nation may be slipping into recession.

"People are beginning to spend less on eating out and traveling," said Rajeev Dhawan, director of the Economic Forecasting Center at Georgia State University. "So the airlines have higher oil prices but also falling demand."

One variable is ticket prices.

Bigger companies with greater "market power" have greater ability to make changes, he said. "You need to raise ticket prices. Do you have market power? That is the key."

The urgency of ticket price hikes will match the spikes in fuel costs.

And since jet fuel is a refined petroleum product, the price of oil accounts for the bulk of jet fuel's cost. Oil prices, which roared to more than $114 a barrel Wednesday, have spurred similar spikes in jet fuel.

A dip will come, but not for awhile, Dhawan said. "I expect higher oil prices till late fall."

Some analysts argue that the price is inflated — but that's a position many have held since oil passed $30 a barrel in the run-up to the U.S. invasion of Iraq.

So now, when they talk about a drop in prices, they mean to $80 or $85. And an increasing number of experts say prices are headed in the opposite direction.

Because global oil production has lately stayed only modestly ahead of demand, worry has grown that current prices will soon seem cheap. If that is true, then airlines can try to hedge or buy in bulk and still lose ground, said economist Lester Lave of Carnegie Mellon.

"Over the next three years, I think the world demand for oil is clearly increasing — see India and China," Lave said.

That will only put more pressure on airlines to increase efficiency and revenues, he said.

Consolidation of the industry does make increases more likely: The fewer the competitors, the fewer the options for a flier.

Yet a series of attempts to boost prices — often in exchange for better space or premium service on the place — has failed, Lave said.

That puts even a huge, merged airline in a bind,

"I don't think we can ever go back," he said. "I think there would be intense resistance to large price increases."