The skies won't be so friendly to your wallet this summer

Leisure air tickets were running 9% higher for domestic travel compared with last year in the four weeks ending May 9, said Bob Harrell, president of New York-based Harrell Associates, which tracks these fares.

Prices for airline tickets recently sold by Orbitz for international travel June 1 through Aug. 31 were up 13% over last summer, the Internet travel seller reported.

Starting in June, round trips between Los Angeles and Europe will typically cost $1,000 or more, travel agents report, compared with some winter prices that dipped below $400.

In July and August, expect to pay nearly $600 or more for round trips to Hawaii from Los Angeles, about twice what they cost in winter, according to the "Lowest Fares" chart published in the Times' Travel section.

Even now, the cheapest fares are fast disappearing.

When I asked Kathy Sudeikis, president of the American Society of Travel Agents, based in Alexandria, Va., what's hot in travel this summer, she responded: "What's not hot is waiting [to book]. Those airfares are only going to go up."

She added, "If you don't have to travel in June, July or August, don't." Other industry insiders offered the same advice.

There are many reasons for the high cost of flying this summer, but they come down to one principle: When demand for a product increases and the supply doesn't, prices go up.

Summer is always a peak travel season, as millions of families with children strive to squeeze vacations into the same few weeks. And passenger traffic is already up this year — more than 5% in the first quarter, according to the Air Transport Assn.

Meanwhile, airlines, for the most part, aren't adding flights. Total takeoffs were about the same in the first quarter this year as last, the ATA reported.

Awash in red ink and wounded by high fuel prices, the so-called legacy carriers, such as Continental, Delta, Northwest, United and US Airways, can't afford to fly with empty seats. So they just fly fuller.

The picture for travel in the U.S. seems somewhat better than for Europe. Taking advantage of their financially weaker competitors, low-cost carriers such as JetBlue and Southwest are adding flights. That puts pressure on prices.

Here's how summer airfares are shaping up, region by region:

Europe: "If you find anything less than $1,000 for an LAX-London round trip, run — don't walk," said Brian Clewer, who owns Continental Travel Shop, an airfare consolidator in Santa Monica. "If it's much less than $1,000, it's too good to be true."

One factor: Europeans, drawn by the cheap dollar, are coming here in droves.

The lowest LAX-London base fare Clewer has seen for this summer is $728, versus $699 last summer. But the real problem is that by Easter, the lowest fares were gone.

Just how many of the cheap seats there were is hard to say; this is a closely guarded secret in the airline industry. But given how quickly the low fares sold out, Clewer figures there were far fewer than last summer.

On top of the base fare, taxes, fees and up to $60 in fuel surcharges can add more than $175 to a transatlantic ticket.