MILWAUKEE -- The Astros' move to the American League in 2013 will make Interleague Play a yearlong affair.Major League Baseball Commissioner Allan H. "Bud" Selig on Thursday formally announced the Astros' move, a shift that will leave each league with three five-team divisions and necessitate at least one AL vs. National League match-up on days that every team is active. Those include Opening Day, the final day of the season and Fridays, Saturdays and Sundays all season. Some have dubbed it perpetual Interleague Play, and it means that Felix Hernandez could be batting for the Mariners on Opening Day in, say, San Diego, or that the Phillies could be employing a designated hitter in Texas for a season finale with the NL East on the line. Initially, Selig conceded, he did not like the idea. But he was won over by the benefits of a 15-15 split, including eliminating the inequities of a four-team AL West and a six-team NL Central. "It won't be perfect -- and no schedule is perfect," Selig said. "But this will be very good." Selig also on Thursday announced the addition of two more Wild Card teams as early as 2012, part of what he called a "historic day" of Owners Meetings at Milwaukee's Pfister Hotel. On the scheduling front, many questions remained unanswered. Among them were just how many extra Interleague games each team will play, whether the home-and-home rivalry series would remain and whether MLB continues its unbalanced schedule, in which teams play more often within their own division. Selig said MLB's scheduling committee is working on a series of options. That group is headed by Phillies general partner, president and chief executive officer David Montgomery and MLB senior vice president Katy Feeney. He urged patience while that group works out the best solution. How might it work? A number of scenarios have been proposed by observers outside of MLB's process. In a proposal advanced by USA TODAY, a team would play 16 games against each of its division rivals, eight games against each of the other 10 teams in its league, three games against each of the teams from a division in the opposite league, plus three games against a natural Interleague rival. The benefit of this scenario is that, besides three games, all of the teams in a division would play the same schedules. Another possibility would be to eliminate the unbalanced schedule and go to 10 games against each of the other 14 teams in your league (144 games), plus 18 Interleague games. In reality, more Interleague games may be needed to make the schedule work for all 30 teams. The Los Angeles Times reported this week that teams are expected to play 72 games -- 18 each -- against division opponents, 60 against teams in their league's other two divisions and 30 Interleague games. "I've looked at a lot of sample schedules and it looks good," Selig said. "Maybe the difference will attract people." Interleague Play has consistently boosted attendance since it was introduced in 1997. Teams drew an average of 18.2 percent more fans for Interleague Games in 2011 than they did during the first three months of intraleague games, though weather in April and early May, before the start of Interleague Play, likely contributed to the smaller early-season crowds. Since its inception, Interleague Play has drawn 12 percent more fans than intraleague games -- an average of 33,285 fans per game compared to 29,716. "Over the past 15 years, I think you can safely say it's been popular," Twins general manager Terry Ryan said. "We have the six games every year with the Brewers, which we like because it was an old rival in the American League." But an expansion of Interleague Play will force GMs to take a fresh look at their rosters. For AL clubs, it will generally mean fewer chances to employ a designated hitter. For NL clubs, perhaps a premium on bench players with potent bats. Just how many Interleague Games are added will determine how those evaluations shift. "It will be interesting to see how teams start configuring their rosters," said Rangers assistant GM Thad Levine. "For us, we would be in good shape with a Michael Young, a player who can fit all over in the field. But would it change things for a club with a Big Papi [David Ortiz, a true designated hitter]? I'm sure clubs will be watching to see how this works out." Club owners will also been watching. Brewers principal owner Mark Attanasio has heard varying arguments from colleagues about a current structure that has the Brewers playing in a six-team NL Central. "Mathematically, the argument is that if there's five of us, it's easier to compete than six of us," Attanasio said. "That's never excessively preoccupied us. We feel like you have to win 88-plus games to get there, no matter how you do it ... and what I might feel as an individual owner may be different when it rises to a baseball issue." As a baseball issue, Selig argued strongly that the realignment made sense. And he dismissed the notion that year-round Interleague Play will water down the excitement that accompanies an AL vs. NL World Series by arguing that the same thing happens in the NFL and the NBA, where teams play across conferences throughout the season. If MLB follows the same timeline as in recent years, the 2013 schedule will be released next September. "I'm proud of the changes, but you want to be sure you're always doing the right thing," Selig said. "This is a thing we've studied for a long time."