Jason Bay admits that he had no idea what to expect from his first time in a free-agent walk year. Now in the final season of a four-year, $18.25 million deal he signed while with the Pirates, he was curious whether he might start viewing his performance through the lens of dollars and cents rather than the state of his team. He wondered whether slumps might be more challenging, whether the element of the unknown would affect his on-field performance.

As has been the case with so many other uncertainties in his time with the Sox, Bay resolved those questions to his satisfaction. Because he is on a team where winning is not just an expectation but a mandate, it became easy for him to set aside those sorts of personal considerations.

“I have actually been pleasantly surprised the entire year,” said Bay. “I will be the first to admit it, I’ve said it before, I didn’t really know how I would react. Would it be the same or would it be different, being in my first contract year, so to speak.

“To be honest with you, when things were going well I didn’t think I was going to break the bank and when things got real bad I wasn’t thinking I’ve ruined my season by any means. I am pretty good at taking things for what it is everyday and I never, even at this point, I am not thinking with every RBI I get I am adding an extra X amount . . . I don’t buy into that stuff.”

Bay will admit that his situation might have been helped by the fact that he got off to such a strong start this year. Through the first six weeks of the season, he was a middle-of-the-order wrecking ball, hitting .301 with a .433 OBP, .657 slugging mark and 1.090 OPS fueled by 13 homers and 44 RBIs in his first 41 games.

He recognized at the time that such numbers were unsustainable — indeed, he would often caution reporters, half in jest, that he was unlikely to drive in 180 runs — but the performance created the framework for a year when he could simply play. That proved valuable when he did hit an inevitable slump, particularly when Bay’s performance sagged for roughly five weeks this season, as he hit .165 with a .581 OPS, one homer and five runs batted in during a 31-game stretch that ran from late-June through the end of July.

Bay has since emerged from that funk. Starting on Aug. 5, he is hitting .297/.393/.642 with an A.L.-leading 16 homers and 42 RBIs in 47 games. Once again, he is performing at an elite level, and so it is increasingly clear that his mid-year dip will not impact the free-agent market for his services come this offseason.

Multiple industry sources expect that bidding for Bay – who is making $7.5 million this year – will reach at least four years at $14-15 million per year this offseason should the outfielder seek to maximize his worth on the open market. Indeed, some have suggested that he could exceed those estimates, both in years and dollars. Certainly, it could help the slugger’s cause that the number of interested teams is expected to be significant.

The Red Sox have already said, at the time that they tabled negotiations just after the All-Star break, that they expect to discuss an extension with Bay following the season, and so a return seems a legitimate possibility, especially given Bay’s often-stated enthusiasm for playing in Boston and his desire to return. Should he test the waters, however, a look at some teams that will have money coming off the books and a potential need for an outfielder who can serve as an impact bat reveals a potentially robust market:

Angels: Vladimir Guerrero ($15 million salary in ’09), Bobby Abreu ($5m), John Lackey ($10m), Kelvim Escobar ($10m) and Chone Figgins ($5.775) will all be coming off the books. If either Abreu or Guerrero departs, the team would have a need to add an impact bat to the lineup.

Cardinals: If Matt Holliday departs via free agency, St. Louis will almost surely seek a middle-of-the-order replacement to complement Albert Pujols. The team also has Troy Glaus’ $12 million coming off the books.

Giants: Free-agents-to-be Randy Winn ($9.25 million), Randy Johnson ($8 million) and Benji Molina ($6 million) could all be moving on. The team could clearly use an outfield upgrade to its offense, after suffering through Winn’s .674 OPS and Fred Lewis’ .743 mark.

Mariners: Adrian Beltre ($13.4 million), Jarrod Washburn ($10.3 million), Miguel Batista ($9.5 million) and Erik Bedard ($7.75 million) are all free agents after this year. The Mariners will likely want to earmark a significant amount of money for Felix Hernandez, and the team has seemed more likely to commit to building through its farm system than free agency, but given that the M’s have exceeded .500 this year, they might look at their brutal left-field production (far and away the worst in the A.L.) and see the potential for a significant upgrade to vault them into contention.

Mets: With Billy Wagner ($10 million) out the door and Carlos Delgado ($12 million) likely close behind him, the Mets have a need for a bat and some money to spend. Bay has demonstrated that he is capable of handling life in a big market, no small consideration to either of the New York teams as they look to fill needs, and there is no question that New York will be looking for a middle-of-the-order hitter.

White Sox: G.M. Kenny Williams recently told reporters, “I don’t like what I see on the free-agent market, and what I do like, it’s going to cost you a No. 1 [draft pick].” It’s not clear which category Bay falls in.

Still, even after the acquisition of Alex Rios, the departure of Jim Thome ($13 million salary in ’09) and Jose Contreras ($10 million) during this season, along with the possible departure of Jermaine Dye this winter ($11.5 million) could leave the ChiSox in a position to invest. Bay doesn’t necessarily fit the mold of the young, athletic players whom Williams has sought recently, and Chicago is somewhat right-handed dominant in its lineup, but Bay’s potential to produce in U.S. Cellular Park is significant, and Williams is nothing if not aggressive.

Yankees: With Johnny Damon ($13 million), Hideki Matsui ($13 million) and Xavier Nady ($6.5 million) all eligible for free agency this winter, the Yankees have more than $30 million in outfield/D.H. payroll that will be peeled away this offseason. Even if New York is committed to keeping a spot for top outfield prospect Austin Jackson, New York could sign Bay and, when the time comes, dump Melky Cabrera to make room for its potential centerfielder of the future. Resources, certainly, aren’t the issue for the potential signing of Bay, who does have the added value of a demonstrated ability to succeed while playing in the A.L. East.