Where the American League’s playoff slate provides a couple teams with far greater certainty — notably, the Red Sox and Tigers — the National League’s pennant chase involves fewer teams overall, yet much greater variability. Where the American League has five teams with a better than one in three shot of winding up in the post-season, the National League has six, and none with anything like the relative statistical certainty that fans in Boston or Detroit might enjoy as we kick off the second half of the season. While he might have to do so from the grave, and change sports, former NFL commissioner Pete Rozelle might smile at the knowledge that with two months to go, both leagues have at least half of their clubs with a 10% shot at playoff baseball in the fall — seven in the AL, nine in the NL.

For the teams in the Senior Circuit harboring October ambitions, the range of choices is no different from those of their AL brethren. They too have to sort out whether they have a shot at contending, and whether they should be buyers or sellers at the end of this month, before trading off (or paying off) multimillion dollar contracts. Whether it’s a matter of retooling a club for its next bid for playoff picture relevance in the years to come, or patching up that bid for contention by filling in the back end of a roster, general managers around the league will be in a frenzy for the next 18 days.

As with Wednesday’s piece on the playoff picture in the American League, we’re looking at a team’s combined shot at making it, taking the wild card into account. All the teams with a realistic shot have two spots they might qualify for, after all. This year’s blurry wild card picture isn’t too dissimilar from last year’s when the race was so crowded that some teams around .500 were obscured by a gaggle of clubs on the fringes of contention, to the point that the Phillies first thought they were out at 47–54 on the morning of July 30. They dumped Bobby Abreu on the Yankees to get out from under his contract, and then had cause to wish that they hadn’t when an 18–10 August put them right back in the thick of things. That turn of events serves as a reminder that while the current playoff odds of clubs like the defending world champion Cardinals or the Giants (Barry Bonds and the 24 dwarves) might be below 3% — slight odds are better than none at all.

The Mets’ recent tailspin might give fans in Flushing some trepidation, but despite a strong pair of challengers in the NL East, they’re still basically in the same boat as the Central-leading Brewers. That’s because both teams — and the Padres and Dodgers in the NL West — seem to be knotted up as far as the quality of their teams and of their performances. All four teams generate nearly identical forecasts of roughly 90 wins apiece, but where the possibilities of a stretch swoon may well kill off the Mets or Brewers entirely, the Padres and Dodgers have the benefit of scenarios where not winning the division doesn’t necessarily mean falling so low that they blow their shots at the wild card. What does that mean? To put it more plainly, the Mets or Brewers would really have to slump to be overtaken by the Braves or Cubs — which is pretty possible, happening about a quarter of the time in the simulated million completed seasons we run — and would almost necessarily slump so badly that it would create an opening for both of the leaders out in the West to make it into post-season play.

That’s the math of it, but the picture is muddied still further by the fact that none of the teams in NL East really have problem-free rosters. The Mets, Braves, and Phillies all have rotations that are a bit of a jumble, and while Omar Minaya and company are anticipating Pedro Martinez’s rehab as a potential cure for what ails them, the Braves have been fruitlessly shopping for a veteran starter for weeks, and that was before John Smoltz’s latest breakdown. What the Braves have that the Mets may well lack is flexibility: Their not having an established first baseman probably frees up John Schuerholz to go shopping, where the Mets simply have to hope that Carlos Delgado’s recent modest hot streak can build into something hot enough to help power a lineup that has seen its outfielders breaking down with the alarming regularity of Spinal Tap’s drummers. If the Braves add an Adam Dunn or a productive veteran first baseman, let alone that starter they need to help them skip guys like Buddy Carlyle and Kyle Davies, and things could get very uncomfortable for the Mets.

In the Central, the division is the Brewers’ to win or lose, but they seem to have already sorted out a number of roster kinks. They’re already reaping the benefits of their decisions to finally promote top rookie Ryan Braun (.350 AVG /.391 OBA /.661 SLG, with a .348 Equivalent Average) to play third, and to make Corey Hart (.298/.368/.508, with a .308 EqA) their everyday right fielder, is being rewarded with an exceptional performances. And where good offensive ballclubs like the Marlins and Phillies are seeing their playoff hopes flounder because of ineffective pitching, the Brewers have a sound rotation, a strong pen fronted by closer Francisco Cordero, and yet another top-shelf rookie in prospect Yovani Gallardo, whom manager Ned Yost has the nice problem of sorting out how to use. The Cubs might sort out their outfield, might find a shortstop, and might have an answer for the catching problems in calling up rookie Geovanny Soto, but that’s an awful lot of wishcasting, even for the Wrigley faithful.

Out West, the proposition is much more simple. It’s another Padres-Dodgers death match, the same as last year, but with the Snakes and Rockies both assembling solid ballclubs, and the Giants at least dangerous as spoilers with a heavily veteran rotation and the Bonds show, it’s one with a relatively combustible set of possibilities. Interdivisional play is sure to get messy, creating hope in Denver and Phoenix where it might seem otherwise unrealistic. The Padres’ blend of a goodenough offense and a strong rotation seems much more stable than the Dodgers’ collection of up-and-coming talents and broken-down big-money mistakes, however. But then, that’s why they play the games, don’t they?

Mr. Davenport is a writer for Baseball Prospectus. For more state-of-the-art analysis, visit baseballprospectus.com.