As difficult a chore as it was for the Chicago White Sox to win the World Series in 2005, the encore proved to be even harder.

"You do the same things you did the last time, but even if you do and keep everybody healthy it's very hard to repeat," White Sox manager Ozzie Guillen said at the Winter Meetings. "Too many things can change. And when you win one year everybody is gunning for you the next [year]. You have that target on your back. You've got to be ready for everybody's best shot every game."

The White Sox won the 2005 World Series and were a popular choice to repeat in 2006, yet missed the playoffs altogether. So did Houston, the team the White Sox swept in the '05 Fall Classic.

The inability to repeat has been the fate of each of the last six World Series winners. The last World Series team to win consecutive crowns was the New York Yankees, who won three straight from 1998-2000, meaning there have been seven different champions the past seven years.

In addition, no team has repeated as a league champion in each of the last five seasons, the longest such streak since 1979-88.

Turnover at the top has been the norm since the millennium turned. Ten franchises made World Series appearances during the 1990s: the Yankees, Braves, Indians, Blue Jays, Phillies, Reds, A's, Padres, Marlins and Twins. The Yankees won three World Series crowns (1996, 1998-99) during the decade and Toronto won consecutive crowns in 1992-93.

Through the first seven years of the current decade, 11 teams have won AL or NL pennants with only the Yankees (2000-2001, 2003) and Cardinals (2004, 2006) winning more than one.

The target on the back cited by Guillen is not the only reason repeat World Series winners have become scarce. More parity and revenue-sharing measures implemented in recent seasons have also been cited as factors.

"Look at our division," said Guillen, whose White Sox play in the American League Central. "There are no easy games in our division. Everybody can beat you. Every night [you're facing] another ace, [Minnesota's Johan] Santana or [Francisco] Liriano, [Detroit's] Kenny Rogers or [Jeremy] Bonderman, [Cleveland's C.C.] Sabathia or [Cliff] Lee, and on and on."

The gap between champion and also-ran in most cases isn't as wide as it had been. Dominating teams have a better shot at repeating, and while there are a fair number of good teams, there has been no dynasty in recent years.

"It's a long way from Opening Day to the World Series," Atlanta manager Bobby Cox said. "So many things can go wrong. Sometimes the difference [between winning and losing] is just a matter of catching a few breaks or not."

Especially with teams so tightly bunched together. The right player added or subtracted from a roster can make a huge difference.

The extra round of playoffs introduced with the Wild Card in 1995 has also made a difference as defending champions have one more hurdle to clear. A Wild Card winner has reached the World Series each of the last five years, winning three. The playoff dynamic can change even more when a team gets hot at the right time, as St. Louis and Detroit did last October.

The Cardinals won the World Series last year despite an 83-78 record, the most losses by a World Series-winning team and the fewest wins by a World Series participant in a non-work-stoppage year since the "Ya Gotta Believe" 1973 New York Mets reached the World Series after going 82-79 during the regular season.

Revenue sharing has helped more small-market teams get into the free agent picture in a bigger way, though the results have largely shown that the biggest payroll doesn't guarantee a pennant.

The bottom line is turnover at the top gives every team added hope that next season could be its year.