Baseball commissioner Bud Selig continues to talk confidently about expanding the baseball playoff field in 2012. But sources tell ESPN.com efforts to make that happen remain bogged down, all because of one thorny little complication: the details.

Wednesday was supposed to be the day the commissioner's office finished a proposed schedule for the 2012 postseason and shipped it to the players' association for consideration. But sources told ESPN.com that deadline wasn't going to be met -- not because talks have broken down, but because fitting two extra wild-card pieces into the postseason puzzle has proved to be more involved than the commissioner has been willing to acknowledge.

The new Basic Agreement stipulates that the commissioner's office and the union need to decide by March 1 whether it will be possible to expand the playoffs this year. Both sides still believe that deadline can be met.

However, multiple sources continue to tell ESPN.com that it's not yet safe to say that adding two wild-card teams for 2012 is "pretty definite," as Selig suggested to USA Today this week.

Here are the major complications:

• The regular season is scheduled to end on a Wednesday (Oct. 3), and the World Series will start exactly 21 days later, on Oct. 24. It isn't feasible at this point to change either of those dates.

• The division series are now tentatively scheduled to begin Saturday, Oct. 6. So the schedule-makers have to figure out a way to jam two one-game wild-card showdowns, plus potential tiebreaker games and/or rainout makeup games, into the two days in between.

Keep in mind that it's now far more likely that there would need to be at least one tiebreaker game under this system. Because the difference between finishing first and being a wild-card team will now be so great, the two sides have agreed that it isn't fair to break those ties any way other than on the field.

• Sources say there have been extensive discussions about eliminating a travel day during the division series to create more room for the wild-card round. But in return, the union has told management it would want concessions on start times for games that would be played on back-to-back days in different time zones.

That could mean, for instance, that the New York Yankees or Boston Red Sox wouldn't be able to play in prime time on the East Coast two games in a row -- a possibility that would likely result in strenuous objections from management and baseball's TV partners.

• Start times for the final day of the regular season also could be affected. If it's decided that one or both wild-card games would be scheduled for Thursday, Oct. 4 (the day after the season ends), the union would prefer to have Wednesday games involving the affected teams moved to the afternoon, sources said.

At this point, it hasn't been decided whether the two wild-card games would be played on the same day or whether one league would tentatively play Thursday and the other would play Friday.

• However, moving a number of night games to Wednesday afternoon on the final day of the regular season would make it more difficult to duplicate the excitement of the last day of the 2011 season -- yet one more potential obstacle to scheduling one or both wild-card showdowns for Thursday.

• Another option is to allow for last-minute flexibility in scheduling days and times for all of these games, to help deal with travel and other challenges that can't be anticipated in advance. But that creates complications for fans and broadcast partners that all concerned would like to avoid.

Many of these concerns would disappear in 2013, because the regular-season schedule would be constructed to account for the addition of the new wild-card round. But because the 2012 schedule already had been announced before talks about this postseason began, there are no easy solutions to these issues if Selig is "adamant," as one source described him, about expanding the postseason field for this year.

Despite the numerous complications, all parties describe the two sides as making a serious effort to make these changes work for this year. But the various hang-ups have turned out to be so difficult to resolve that one source said this week: "I really don't know if this is going to get done."

"All of this is solvable," one management source said. "It just depends what consequences you're willing to accept."

Jayson Stark is a senior baseball writer for ESPN.com.