There have been thousands of trades across Major League Baseball since the 30-team era began with the addition of the D-backs and Rays for the 1998 season. But they aren’t distributed evenly.

Sometimes, two teams go a decade or longer without completing a single swap. Others seem to be combining constantly for trades, whether due to needs that conveniently match up, strong front office relationships or other factors.

With that in mind, here is a breakdown of MLB’s most prolific trade partners of the aforementioned 30-team era, with a big assist from Baseball-Reference’s franchise trade history tool.

It should be noted that this is a simple measure of how many trades have been made, not how big those trades have been, and they can include anything from a cash deal for an unheard-of Minor Leaguer, to a swap of superstars. For example, this list won’t include the Dodgers-Red Sox pairing, but even though those two have traded a modest seven times since the start of the 1997-98 offseason, three of those were genuine blockbusters featuring Manny Ramírez (2008), Adrián González (‘12) and Mookie Betts (‘20).

Still, this list of top dealmakers includes plenty of firepower.

1) A’s and Blue Jays: 27 trades
Notable example: Oakland traded Josh Donaldson to Toronto for Franklin Barreto, Kendall Graveman, Brett Lawrie and Sean Nolin (Nov. 28, 2014)

Billy Beane took over as Oakland’s general manager on Oct. 17, 1997, right at the beginning of the 30-team era we are covering here. Under his watch, the A’s have made more total trades (300 of them) than anyone else as Beane has looked for ways to keep the team competitive with limited resources. Many of those deals have done the job -- the one noted above being a painful exception -- and the A’s have made 10 postseason appearances with Beane at the helm.

While Beane has made lots of deals with lots of organizations and a parade of rival executives who have come and gone during his tenure, his volume of work with Toronto stands out. Few of the swaps have created a lasting impact, beginning with Oakland’s ill-fated acquisition of third baseman Ed Sprague at the 1998 Trade Deadline. But that’s the nature of the business, and there have been exceptions, with the Blue Jays landing a future MVP in Donaldson, and the A’s snatching a future star closer (Liam Hendriks) a year later.

2) Mariners and Padres: 23 trades
Notable example: San Diego traded Ty France, Andrés Muñoz, Luis Torrens and Taylor Trammell to Seattle for Austin Adams, Dan Altavilla and Austin Nola (Aug. 31, 2020)

It’s really more about quantity than quality for these “Vedder Cup” foes, with the Padres and Mariners both ranking among MLB’s most trade-happy clubs during this time period. But few players who have changed hands in any of these deals have made a significant impact.

3) Padres and Red Sox: 22 trades
Notable example: San Diego traded Craig Kimbrel to Boston for Logan Allen, Carlos Asuaje, Javy Guerra and Manuel Margot (Nov. 13, 2015)

The two teams were connected when Larry Lucchino left the Padres to become the Red Sox’s president and CEO in 2002 and soon became involved in bringing Theo Epstein from San Diego to Boston. Epstein subsequently worked with his former organization on numerous occasions, including a trade in December 2010 that sent González to Boston for a package including Anthony Rizzo. The Padres GM at the time was Jed Hoyer, who had been under Epstein with the Sox.

The Epstein connection is long gone, of course, but the clubs have continued to deal, with Boston plucking Kimbrel and Drew Pomeranz from San Diego in recent years, helping set up its 2018 championship.

4) Mariners and Rays: 21 trades
Notable example: Seattle traded Lou Piniella and Antonio Pérez to Tampa Bay for Randy Winn (Oct. 28, 2002)

Yes, that’s right. These clubs once pulled off a trade involving a manager, with Tampa Bay giving up a 2002 All-Star outfielder in Winn for the purposes of installing Piniella in the dugout. The ploy was not particularly successful -- Piniella lost 90-plus games in each of his three seasons in Tampa Bay -- but these geographically distant teams have continued to work together. The pace has increased of late, with 13 deals in the six-plus years since Jerry Dipoto arrived in Seattle, including a December 2018 three-teamer that sent Carlos Santana back to Cleveland, Edwin Encarnación to Seattle (temporarily) and Yandy Díaz to Tampa Bay.

5-T) A’s and Royals: 19 trades
Notable example: Oakland traded Ben Zobrist and cash to Kansas City for Sean Manaea and Aaron Brooks (July 28, 2015)

For about the first 30 years of the Royals’ existence, they made just one trade with the club that called Kansas City home before them. But the Beane era has brought a bonanza. The Zobrist deal, of course, helped the Royals win the 2015 World Series, while also landing the A’s a future rotation piece in Manaea.

But even before that, there was quite a bit of action. Notable Moneyball-era A’s such as Johnny Damon, Mark Ellis and Jeremy Giambi arrived in the Bay Area via K.C., and the A’s also had their hand in the three-team trade that sent Carlos Beltrán from the Royals to the Astros in 2004.

5-T) Blue Jays and Phillies: 19 trades
Notable example: Toronto traded Roy Halladay and cash to Philadelphia for Travis d’Arnaud, Kyle Drabek and Michael Taylor (Dec. 16, 2009)

This pairing got the Phillies a future Hall of Famer at the peak of his powers, with Halladay immediately winning his second Cy Young Award and throwing a perfect game and a postseason no-hitter with his new club in 2010. But it wasn’t the first time Philly landed a playoff hero from Toronto. At the end of August 2008, the Jays moved well-traveled slugger Matt Stairs to the Phillies in a waiver deal, and Stairs’ pinch-hit, go-ahead homer late in Game 4 of the NL Championship Series against the Dodgers helped propel his new club to a championship.

5-T) Cubs and Rangers: 19 trades
Notable example: Chicago traded Ryan Dempster to Texas for Kyle Hendricks and Christian Villanueva (July 31, 2012)

These are both top-10 teams in terms of trade volume, and it’s quite possible Epstein would not have built a drought-busting team on the North Side without Texas' Jon Daniels. Besides stealing Hendricks -- then in Class A Advanced -- Epstein also acquired relievers Carl Edwards Jr. and Justin Grimm at the following Trade Deadline in exchange for Matt Garza. All three pitchers played sizable roles on the Cubs’ 2016 championship squad.

5-T) A’s and Padres: 19 trades
Notable example: Oakland traded Ramón Hernández and Terrence Long to San Diego for Mark Kotsay (Nov. 26, 2003)

The pace has perhaps slowed a bit since A.J. Preller took over the Padres in August 2014, but the two sides have gotten together for two trades since December 2019.

10-T) A’s and Cubs: 18 trades
Notable example: Chicago traded Josh Donaldson, Sean Gallagher, Matt Murton and Eric Patterson to Oakland for Rich Harden and Chad Gaudin (July 8, 2008)

Here are the A’s, and Donaldson, yet again. In this case, though, Donaldson was an A-ball catcher and Harden an elite pitching talent who was brilliant for the NL Central-winning Cubs down the stretch. Oakland got the long-term benefit from that one, and while a July 2014 deal for Jeff Samardzija that sent Addison Russell to Chicago did not work out so well directly, the A’s soon flipped Samardzija to the White Sox for a package featuring Marcus Semien and Chris Bassitt.

10-T) Indians and Pirates: 18 trades
Notable example: Cleveland traded Brian Giles to Pittsburgh for Ricardo Rincón (Nov. 18, 1998)

The mid- to late-90s Indians were so loaded that it took this trade for Giles to get a crack at a full-time job, and he proceeded to post a 1.018 OPS in five seasons with the Bucs before being sent to San Diego for Oliver Pérez and another pre-breakout outfielder, Jason Bay. None of the teams’ swaps since have come close to making that sort of impact.

10-T) Rangers and White Sox: 18 trades
Notable example: Texas traded Lance Lynn to Chicago for Dane Dunning and Avery Weems

There haven't been many trades of consequence between these two sides, with Chicago's recent deal for Lynn standing out as the most notable example.

HONORABLE MENTIONS

17 trades

• Pirates and Yankees: Their February 2012 trade rejuvenated A.J. Burnett’s career and helped the Bucs snap a long postseason drought in ‘13.

16 trades
• Blue Jays and Indians: They have traded 12 times just since 2010, including yet another Donaldson deal.

• Cubs and Marlins: Dontrelle Willis, Derrek Lee, Juan Pierre, Carlos Zambrano and Dan Haren are just some of the big names these teams have swapped.

• Dodgers and Rays: These 2020 World Series opponents have been frequent trade partners since Andrew Friedman left Tampa Bay's front office to join the Dodgers in 2014.

• D-backs and White Sox: Who can forget that Hall of Famer Roberto Alomar was traded to the White Sox in back-to-back seasons, including from Arizona for the final 18 games of his career in 2004?

• A’s and Nationals: Mike Rizzo has averaged more than a deal per season with Beane since becoming Washington’s GM.

• D-backs and Yankees: Their biggest deals have been three-teamers with Detroit in 2009 (featuring Curtis Granderson and Max Scherzer) and ‘14 (Didi Gregorius, Robbie Ray).

• Indians and Red Sox: They still have played more postseason games against each other (19) in this time period.

• Orioles and Phillies: Their latest trade came prior to the 2021 Deadline, when Philadelphia brought back Freddy Galvis.

• Padres and Yankees: The road between San Diego and the Bronx is known as the Chase Headley Highway.

• Pirates and Phillies: Charlie Morton, Corey Dickerson and Joaquin Benoit are the most notable players to be traded between these two clubs.

For teams who have not yet appeared on this list, here is the top trade partner or partners for each one in the 30-team era.

• Mets: 15 (Dodgers and Royals)

• Reds: 14 (Rockies)

• Rockies: 14 (A’s, Reds)

• Angels: 14 (Rays)

• Braves: 13 (Dodgers)

• Brewers: 13 (Blue Jays)

• Cardinals: 12 (Indians)

• Tigers: 12 (Braves)

• Astros: 11 (Blue Jays and Rays)

• Giants: 11 (Yankees)

• Twins: 10 (Red Sox, Yankees)