Fly US Airways in and out of Philadelphia from Pittsburgh on Jan. 4, and the nonrefundable round-trip fare would be $118, before taxes.

Take those same nonstop flights a week later, and the US Airways fare jumps to $698.

Information on fares was collected Monday afternoon on the airline's website.

Why the reason for the change?

Southwest Airlines, the only major competitor to US Airways on that route, will end its nonstop service between the two cities on Jan. 8.

Airline analyst Michael Boyd, who had predicted a big jump in Pittsburgh-Philadelphia airfares once Southwest ended service, wasn't surprised by the news.

"That's what happens when you have less competition," he said Monday. Mr. Boyd is president of Boyd Group International, an airline consulting firm based in Evergreen, Colo.

Neither was JoAnn Jenny, a spokeswoman for the Allegheny County Airport Authority, which operates Pittsburgh International Airport. "We had asked the community to support those Southwest flights, but passengers weren't choosing them," she said. "The company could not afford to keep operating."

US Airways flights to Philadelphia were about three-quarters full, while Southwest planes were barely half-filled. "Southwest was dying on that route," Mr. Boyd said.

Don't blame Pittsburgh passengers for the loss of that airline's service, he said. They were, at least in the short term, making intelligent decisions in picking the dominant carrier. US Airways offered advance seat selection, early boarding and frequent-flier miles through the Star Alliance system, which could be redeemed on a number of major airlines.

"If fares are the same, you'd tend to go with US Airways," he said. "The Southwest product wasn't competitive with business travelers who want to build frequent-flier miles and know where they are sitting."

The loss of competition and jump in prices, however, didn't sit well with Witold Walczak, who found out last week that the cost for his once- or twice-a-month flights across the state would increase more than five-fold in January.

"Unless you are or work for the one percent, these prices are prohibitive," he said. "This is price gouging of the worst sort ... the free market is really sticking it to the little guy.