First it was fuel. Now it's soft demand.

Whatever the reason, departures from Salt Lake City's airport to other U.S. cities are down almost 12 percent since January.

Capacity -- airline seats available to fly passengers -- is off more than 10 percent, according to a report commissioned by the Salt Lake City International Airport.

Twenty-one destinations have been eliminated, according to SH&E, an aviation consulting firm that prepared the report for the airport. Flights to dozens of cities have been curtailed.

Taken together, fewer departures, fewer seats and fewer routes add up to fewer planes, crowded aircraft and fewer options for flying when it's convenient. Perhaps not surprisingly, passenger numbers are off 4.6 percent.

"It's not unlike a favored government service that you are used to that's now not there. Certainly, people have been inconvenienced," said Natalie Gochnour, chief operating officer of the Salt Lake Chamber.

Delta Air Lines, the dominant carrier at Salt Lake's airport, was the biggest cutter. It's departures and available seats are down 14.4 percent and 13.5 percent, respectively. Delta's westernmost hub is at the airport.

But Delta wasn't alone. Continental, Frontier, JetBlue, United and US Airways cut service, too.

"The conclusion would be that the carriers right-sized to account for the high price of fuel and the softening demand for travel in these extremely fragile economic conditions," said David Castelveter, a spokesman for the Air Transport Association, a trade group that represents most U.S. airlines.

If there is any good news, it's that Salt Lake City International isn't suffering more than most big airports. Since early last year, airlines have cut domestic flights deeper at 14 hub airports, less so at 11 hubs, according to ATA.

"For our size and operation, we are doing much better than a lot of other airports across the country," said airport spokeswoman Barbara Gann.

With crude oil prices approaching $100 a barrel at the beginning of this year, Delta began cutting capacity across its network of U.S. routes. In January, the airline said it was halting flights from Salt Lake to six airports and was trimming the number of daily runs to another 12 cities.

Delta's plan was to reduce domestic capacity by 5 percent this year. But as oil prices spiked ever higher, the airline expanded its goal. With two weeks left in the year, Delta has cut 13 percent of its domestic capacity since January. Its Salt Lake capacity is down 13.5 percent.

Expect more reductions. Oil prices have plummeted more than 70 percent since peaking at $147 per barrel in July. But last month Delta said passenger demand for seats began to slow in the fourth quarter. It said domestic capacity in 2009 will be reduced 8 percent to 10 percent compared with 2008, while international capacity will be reduced 3 percent to 5 percent next year compared with this year.

While Salt Lake likely will see more reductions, it's unclear how deep they will be.

"While we have not announced market adjustments yet, we will be making tweaks to the schedule throughout the year," said Delta spokesman Anthony Black.