Baseball is the most expensive of the five sports included in the study. MLS is the least costly, requiring minimum total personal income of $13.9 billion. The income thresholds for the other leagues are $36.4 billion for the NBA and $37.3 billion each for the NFL and NHL.

Los Angeles has been out of the NFL since 1995, when the Rams and Raiders moved to St. Louis and Oakland, respectively.

The state of California recently approved a proposed 75,000-seat stadium in Industry, a suburb of Los Angeles in the San Gabriel Valley. The facility, which would be developed by Majestic Realty Co., is expected to be privately funded.

The NFL has not announced any plans to expand, so Majestic Realty is setting its sights on luring a team to Los Angeles from another city. Its list of prospective targets includes the Buffalo Bills, Jacksonville Jaguars, Minnesota Vikings, Oakland Raiders, St. Louis Rams, San Diego Chargers, and San Francisco 49ers.

The only sport currently proceeding with expansion is MLS, which is adding franchises in Philadelphia, Portland, Oregon, and Vancouver during the next two seasons. It could easily keep growing, with 42 additional markets having the financial wherewithal to support pro soccer.

The study analyzed TPI data to generate capacity scores for each market in each sport. A score of 100 indicates that an income base is strong enough to support a team, while a reading of between 70 and 99 is a sign of a borderline base that may or may not be adequate.

These ratings were then used to concoct expansion scenarios for MLS and the other four leagues. It identified Montreal and Rochester, New York, for example, as ideal soccer markets, given their substantial income bases and long histories of supporting the game. (See the scenarios sidebar for breakdowns for all five leagues.)

The NFL, NBA, and NHL find themselves in similar situations, respectively having 18, 17, and 16 open markets with adequate income bases. But baseball has virtually nowhere to turn, since the TPI required for an expansion or relocated team in that sport is so high.

Just two markets currently outside of MLB have income bases sufficiently large to join its ranks: Riverside-San Bernardino, California, and Montreal. And the latter is tainted because it lost a baseball franchise, the Expos, to Washington five years ago (the Expos were renamed the Nationals).

Overextension is a serious problem in Denver, which has franchises in all five sports. The Denver metropolitan area could use an additional $92.5 billion in total personal income to provide an adequate base for its existing franchises.

This shortfall doesn’t necessarily mean that any of Denver’s teams will move or fold. But it’s a reliable sign that those teams can expect continued volatility in attendance and revenues.

The Denver Broncos perennially rank among the NFL’s attendance leaders, and the Colorado Rockies were a respectable 11th out of 30 MLB teams at the box office in 2009. But Denver’s other three franchises (the NBA Nuggets, NHL Avalanche, and MLS Rapids) finished in the bottom half of their leagues in attendance during their most recent full seasons.

Eighteen other markets are overextended, based on Portfolio.com/bizjournals’ estimates. Included are six areas with TPI deficits larger than $45 billion: Cleveland, Pittsburgh, Tampa-St. Petersburg, Kansas City, Milwaukee, and Phoenix.

Economic capacity was the focus of the study, but other considerations would obviously be important in any decision to expand or relocate a franchise. Among them would be proximity to existing teams, the availability of stadiums or arenas, and unique local factors (such as the prominence of gambling in Las Vegas).

To explore an interactive that breaks down the study's results, click here.