To avoid losing key players in free agency, teams may look to sign them to contract extensions before they get the chance to test the open market.

The Phillies did just that with ace pitcher Zack Wheeler, signing him to a three-year, $126 million extension through 2027. With his five-year, $118 million contract with Philadelphia set to expire at the end of the 2024 campaign, Wheeler would have been eligible for free agency next offseason. At $42 million annually, Wheeler's new deal carries the highest average annual value for an extension in MLB history.

While Wheeler's new deal has a massive annual salary, Mookie Betts’ $365 million extension with the Dodgers is the largest signed by a player in terms of new guaranteed total money added on to a player’s existing contract.

Here's a look at the largest contract extensions in Major League history, in descending order of total dollars. (For a list of the longest contracts -- including free agent deals -- click here.)

1) Mookie Betts, Dodgers -- 12 years, $365 million
Signed in 2020, runs through 2032
The Red Sox traded Betts and southpaw David Price to the Dodgers in a blockbuster trade following the 2019 season, in large part because many expected the former American League MVP to test the market following the 2020 campaign and challenge the recent free agency standards set by Bryce Harper and Manny Machado. But Los Angeles’ front office was able to hammer out a massive extension right as the shortened 2020 season was set to begin, adding on to the record one-year, $27 million contract that Betts and the Red Sox agreed to in January 2020 in order to avoid arbitration.

Making sure Betts stayed a Dodger was a no-brainer decision at the time, and proved even more so once the games got underway. Betts placed runner-up in the 2020 NL MVP Award vote, and then helped lead L.A. to a long-awaited World Series championship with a string of plays with his bat, legs and glove during the postseason.

2) Mike Trout, Angels -- 10 years, $360 million
Signed in 2019, runs through 2030
The Halos made sure the game’s consensus best player -- and one off to an historic start to his sure-to-be Hall of Fame career -- remained in Orange County for the foreseeable future. This deal added on to the two years and $66.5 million that were still remaining on the contract Trout signed in 2014, thus making his new 12-year, $426.5 million deal the richest in North American professional sports history at the time. Trout immediately rewarded the Angels’ faith in 2019 by bashing a career-high 45 home runs and winning his third career league MVP Award.

3) Manny Machado, Padres -- 11 years, $350 million
Signed in 2023, runs through 2033
Machado originally joined the Padres on a 10-year, $300 million contract in February 2019, at the time setting a record for the largest free-agent deal in MLB history (though it has since been exceeded by several other deals). The contract gave him the ability to opt out at the end of the 2023 season, and Machado told reporters during Spring Training that he planned to exercise his opt-out power to test the open market. However, it appears he’ll be staying in a Padres uniform for years to come. The extension will begin in 2023, effectively replacing the six years left on his previous deal with a new 11-year contract running through 2033.

4) Francisco Lindor, Mets -- 10 years, $341 million
Signed in 2021, runs through 2031
Under new owner Steve Cohen, the Mets hinted that the 2020-21 offseason would be a big one in Queens, and they delivered, landing Lindor and right-hander Carlos Carrasco in a trade with Cleveland. Once that deal was done, speculation turned to whether the Mets would be able sign Lindor, a four-time All-Star and two-time Gold Glove Award winner, to a long-term extension. The two sides reached a deal on March 31, the eve of Opening Day. Lindor's 2021 salary of $22.3 million remained unchanged, and the extension -- the richest ever for a shortstop -- took effect in 2022.

5) Fernando Tatis Jr., Padres -- 14 years, $340 million
Signed in 2021, runs through 2034
After a promising but abbreviated rookie year in 2019, Tatis consolidated his promise with an electric performance in the pandemic-shortened 2020 campaign, slashing .277/.366/.571 with 17 homers in 224 at-bats and placing fourth in the NL MVP Award vote. His play was a major reason why the Padres snapped a 14-year postseason drought, and then he thrived under the brighter lights by becoming the third-youngest player to hit multiple homers in a playoff game. While the Padres missed the playoffs in 2021, Tatis finished with an NL-leading 42 homers, plus 25 steals and a .975 OPS in 130 games. Tatis missed the 2022 season with a wrist injury, followed by a suspension for a banned substance, but he returned to post a 5.5-WAR season (per Baseball-Reference) in 2023, making a successful switch from shortstop to right field.

6) Rafael Devers, Red Sox -- 11 years, $331 million
Signed in 2023, runs through 2033
With Xander Bogaerts departing for the Padres in free agency after the 2022 season, the Red Sox put their attention on keeping their other superstar, Devers, in Boston for the long haul. A year before Devers would have reached free agency, the Red Sox reached an agreement with their two-time All-Star third baseman on the largest contract in franchise history. Devers' deal surpasses the seven-year, $217 million free-agent contract David Price signed with the Red Sox in 2016, and the seven-year, $154 million extension Adrián González signed with them in 2011.

7) Giancarlo Stanton, Marlins -- 13 years, $325 million
Signed in 2014, runs through 2028
Baseball had not seen this type of contract -- both in terms of length and total value -- before Stanton put ink to paper following the 2014 season. But the hulking slugger is playing out the majority of this deal with the Yankees, and not the Marlins; Stanton logged the first three seasons of the contract with Miami before the club traded him to New York in December 2017, shortly after he won that year’s NL MVP Award. Stanton didn't enact his opt-out clause after the 2020 season, choosing to stay in the Bronx after some injury-plagued seasons in pinstripes.

8) Miguel Cabrera, Tigers -- 8 years, $248 million
Signed in 2014, ran through 2023
History repeated itself a bit here, as Dave Dombrowski -- the same general manager who signed Miggy to an eight-year, $152.3 million extension shortly after acquiring Cabrera for the Tigers via a trade in 2007 -- made sure Cabrera would stay in Detroit with an even bigger eight-year extension. This extension added on to the remaining two years and $44 million from Cabrera’s previous deal, and briefly positioned the slugger for the highest annual average value in history at $31 million. Cabrera certainly earned a massive extension as he was coming off back-to-back AL MVP awards (including a Triple Crown season in 2012), but injuries took their toll in the latter half of this deal and he retired at the end of the 2023 season. He's one of seven players to produce at least 3,000 hits and 500 home runs in their career.

9) Nolan Arenado, Rockies -- 7 years, $235 million
(One year, $15 million later added onto deal)
Signed in 2019, runs through 2027
Less than one month after Arenado agreed to a then-record one-year, $26 million contract with Colorado to avoid arbitration, he was able to hammer out an extension with the club, adding seven years and $235 million to his existing contract. When the Rockies traded Arenado to the Cardinals prior to 2021 in exchange for left-hander Austin Gomber and four Minor League players, St. Louis tacked another year for $15 million onto the end of the contract in exchange for Arenado agreeing to waive his no-trade clause. He also gained the ability to opt out of his deal after the 2022 season, although he later chose not to do so.

10) Joey Votto, Reds -- 10 years, $225 million
Signed in 2012, ran through 2023
Votto won the 2010 NL MVP Award and the Reds signed a three-year deal after that season in order to avoid arbitration. But eventually, Cincinnati rewarded its superstar in grand fashion. Votto paced the Senior Circuit in his specialty, on-base percentage, five more times after signing this extension and nearly won another NL MVP in 2017, finishing second to Stanton. After a pair of injury-plagued seasons, Votto became a free agent when the Reds declined his $20 million club option for 2024.

11) Clayton Kershaw, Dodgers -- 7 years, $215 million
Signed in 2014, signed additional extension in 2018
The reasons to give Kershaw a massive extension didn’t require too much analysis. The southpaw had already captured two NL Cy Young Awards through his age-25 season and finished runner-up in another campaign, and he had lowered his career ERA in each successive season since making his debut -- a trend that would continue all the way through 2017. The Dodgers looked really smart immediately after Kershaw signed in January 2014, as he went on to win both his third Cy Young and the NL MVP Award after going 21-3 with a 1.77 ERA and 239 strikeouts. He and L.A. finally captured their long-awaited World Series championship in 2020.

12) Derek Jeter, Yankees -- 10 years, $189 million
Signed in 2001, ran through 2010
This was the culmination of a prolonged negotiation process between Jeter and the Yankees that spanned 13 months. At the time, it trailed only the $252 million contract that Alex Rodriguez -- Jeter’s future teammate -- signed with the Rangers in terms of the richest contract in baseball history. After signing in February, Jeter helped lead the Yankees to their fourth straight World Series appearance (earning his Mr. November moniker that fall) and continued his run as one of the most beloved players in Yankees history for the rest of the decade and beyond. He was elected to the Hall of Fame with 99.7% of the Baseball Writers' Association of America vote in 2020.