If there’s been a singular surprise this season – other than the Yankees’ failures – it’s been the success of the Baltimore Orioles.

At present, the Orioles hold a three-game lead in the AL East and are on pace to win 96 games by season’s end. While the O’s have enjoyed some impressive individual pitching performances (Eric Bedard, Bruce Chen, B.J. Ryan, and John Parrish chief among them), it’s the offense that’s driving their success.

Baltimore leads the majors in batting average and slugging average and ranks second in runs scored, thanks largely to the historic efforts of second baseman Brian Roberts and shortstop Miguel Tejada. In fact, Roberts and Tejada are on pace to establish themselves as one of the most imposing offensive tandems in the annals of the game.

Roberts has notched a batting line of.369 AVG/.449 OBA/.646 SLG, while Tejada is hitting .328/.373/.639. Needless to say, those are impressive numbers, particularly by middle-infielders’ standards. To gain further perspective on what Roberts and Tejada are in the midst of accomplishing, let’s use the Baseball Prospectus statistic, Value Over Replacement Player. VORP measures, in runs, the level of offensive production provided by a player over what could be expected from a readily available fill-in (e.g., the bench player, the minor league veteran, the not-quite-ready prospect, or the waiver claim). Generally speaking, offensive production and playing time are the two primary components of VORP.

As of today, Roberts has a VORP of 41.2, which easily makes him baseball’s most productive second baseman. As for Tejada, his current VORP of 37.8 leads all shortstops by a wide margin. Pro-rated to a full season, Roberts is on pace for a VORP of 113.1, while Tejada is heading for a VORP of 103.8 – that’s a total projected middle-infield VORP of 216.9. Should that come to pass, Tejada and Roberts would be the most productive second base-shortstop combo since 1901 – by a comfortable margin. Presently, that list is topped by Rogers Hornsby and Specs Toporcer of the 1922 Cardinals, who combined for a VORP of 169.6, followed by Chuck Knoblauch and Derek Jeter of the 1999 Yankees, who teamed up for a VORP of 152.6. So if trends hold, it would be a rout for the O’s duo.

Given such a staggering margin, it’s perhaps more useful to think of Roberts and Tejada in terms of other great teammates, without confining the comparisons to middle infielders. As you can see from the above chart, if Roberts and Tejada continue on their current pace, they will finish the season as the third most productive offensive duo of the past century, more potent even than three Ruth-Gehrig iterations. Suffice it to say, that’s rarified statistical air.

Of course, arguments framed around “on pace to” observations are quite tricky. So we must ask: How likely is this to continue? In the case of Tejada, he’s having the finest season of his career, but he’s also a proven performer. He was the 2002 AL MVP as a member of the Oakland A’s and is in the midst of his sixth consecutive All Star-caliber season. At age 29, Tejada may very well be enjoying his peak season. As such, it’s not unreasonable that he’ll maintain a level of production similar to his current one through September.

The real question is whether Roberts can keep it up. Coming into this season, he was a career .264/.328/.360 hitter in four big league seasons. Obviously, he’s drastically exceeding those numbers. Coming up through the minors, Roberts flashed good on-base skills, but nothing remotely resembling the power spike he’s enjoyed in 2005.At age 27, he’s in “prime season” territory, but there’s still little in his statistical dossier to auger such an incredible performance.

As for his power numbers, Roberts did hit 50 doubles last season, which, in some cases, points to a developing power stroke. The logic goes that once a young player gains strength and refines his stroke, some of those doubles will turn into homers. Sure enough, Roberts’s doubles pace is down this season, but he’s also on target for 30 homers, which would be 18 more than his career total entering this season.

The real story for Roberts may be that his batting average is exceeding his pre-2005 career average by more than 100 points. Batting average is known to be the traditional offensive statistic most prone to random variation, and it’s the prime underpinning of quite a few “fluke” seasons throughout baseball history. That is very likely the case with Roberts.

Still, Roberts has shown improved plate discipline (he’s tied for eighth in the AL in walks) and excellent raw power indicators. Though he is playing way over his head, there are enough signs here to assume that he’s made legitimate strides as a hitter. The two, after all, aren’t mutually exclusive. Even accounting for anticipated decline, Roberts will likely wind up with MVP-level numbers on the season. We’ll probably never again see such a performance from him, but it’s also likely that he’s turned out to be a much better player than his statistical history would’ve led you to believe.

As the season deepens, a moderate decline from the duo is to be expected, but there’s still a fine chance that Roberts and Tejada will wind up as the most potent second base shortstop combo of the last 100 years. If they do, the Orioles could conceivably hold off the powers that be in the AL East for their first postseason appearance since 1997.

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