If the Orioles are going to sign Brian Roberts to an extension, four years is the perfect length.
Let's start with what they get in Roberts. He is perhaps the third-best second baseman in baseball behind Chase Utley and Dustin Pedroia, so he affords the Orioles a significant advantage over other clubs at a position that's thin on talent.
Roberts will be 31 this season and 35 in the last year of the reported deal. Because he's a multi-faceted player with incredible devotion to fitness, logic says he should age well. If he follows the normal arc for a second baseman of his quality, he will not be as good over the next five years as he was over the past five, but he also won't fall off the table.
Here's the tricky part. This club is at least two years away from posing a real threat to the good teams in the American League East, so Roberts' salary isn't likely to buy the Orioles much short-term advantage. On the other hand, if they're going to extend him, they want him to be around when the club has a chance to be pretty good between 2011 and 2013. Roberts might not be a star in the last few years of the extension, but even if he's an above-average second baseman, he would be helpful.
Remember also that this team is cheap right now and likely to get cheaper when Melvin Mora, Aubrey Huff and others hit the end of their deals next offseason. In that context, locking up one of the few real stars makes even more sense.
Look, if the Orioles had been able to flip Roberts for a high-end prospect or two, that would have been great. But Andy MacPhail listened to offers for more than a year and none struck his fancy.
The Orioles had no business parting with an asset as significant as Roberts for anything less than front-line talent. In the absence of such an offer, this extension looks like the best solution.