PHILADELPHIA — Combine popular players, big markets, a team on a hot streak and a trio of long-suffering cities desperate for a World Series champion and what do you get?

If you're Major League Baseball, a problem. But it's a good one to have.

The traditionally moribund Philadelphia Phillies, the lovable loser Chicago Cubs and the sometimes hapless Cleveland Indians are in the playoffs. So are the New York Yankees, Boston Red Sox and Los Angeles Angels, while the Colorado Rockies are riding a furious late-season rally and flying high off a win in a wild-card tiebreaker.

And their merchandise is selling so fast that Major League Baseball is having a hard time keeping up.

With a regular season that went down to the final weekend — and beyond, in the case of the Rockies, who needed a one-game playoff to win the wild card — the confluence of big markets, rabid fan bases and potential storybook endings is pushing memorabilia sales.

The urge to buy was strong in the playoff cities on Wednesday.

Across the street from Coors Field in Denver, the store Sportsfan still hadn't received Rockies wild card T-shirts or hats. Assistant manager Clayton Reed said the phone has been ringing off the hook with requests for merchandise.

"We're not used to this stuff in September," he said.

"So, yeah, it's really hard to keep stuff in here on a constant basis."

For franchises with traditionally strong sales like the Yankees and Red Sox, that isn't unusual, according to Mike May, director of media relations for the Sporting Goods Manufacturers Association.

But it could get bigger if one of the Cinderella teams wins the Series.

"In these other markets — Phillies, Cubs, Rockies — whatever's not nailed down is going to go," he said.

In a year with relatively ho-hum playoffs, MLB might see the postseason produce about 5 percent of its merchandise sales, said MLB official Howard Smith. This year, it could be as high as 20 percent.

While the league does not release sales figures, the manufacturers association reported total sales of MLB merchandise was $3.1 billion in 2005, the last year for which figures were available. That was up from $2.9 billion in 2004, when the Red Sox won the World Series and touched off a buying frenzy, Smith said.

May said fans get swept up in the excitement and have to be a part of it.

"When people get caught up in the excitement of a winning team, especially in the case of the Red Sox and White Sox (the 2005 World Series champs), who had not tasted victory in decades, people feel, 'If I don't buy now, I'll never get a chance to buy them as a winner, because it may be just as long before they win it again.' "