Fells' two-year deal, which was first reported by NFL Network, includes $4 million in the first year, the source told ESPN. Fairbairn's contract is for four years, a source told ESPN, confirming a report by the Houston Chronicle.
Fairbairn's contract is worth $17.65 million and includes $9 million fully guaranteed with $10.45 million over the next two years, a source told ESPN's Adam Schefter.
Fells, who turns 34 on April 22, is coming off the best season of his six-year NFL career.
The former professional basketball player had a career-best 34 catches for 341 yards and seven touchdowns for Houston in 2019, establishing a strong connection with quarterback Deshaun Watson while setting a franchise record for touchdowns by a tight end in a season.
Fairbairn made 80% (20-of-25) of his field goals last season, which ranked 20th in the NFL. He struggled with extra points early, missing four in four games. However, after missing one against the Kansas City Chiefs in Week 6, Fairbairn only missed one of his 27 remaining attempts during the regular season.
Fairbairn, who turned 26 in January, has been Houston's starting kicker since the 2017 season, when he beat out veteran Nick Novak.
In three seasons, Fairbairn has made 83.7% (77-of-92) of his field goal attempts, with a career long of 51 yards. He has made 91.7% (111-of-121) of his career extra point attempts.
Houston signed Fells to a one-year deal during the 2019 offseason. He has also played for the Arizona Cardinals, Detroit Lions and Cleveland Browns since entering the league as an undrafted free agent in 2013.
Fells, who has mostly contributed as a blocker during his six seasons, has 102 career catches for 1,171 yards and 17 touchdowns.
Fairbairn signed with the Texans as an undrafted free agent in 2016, but he spent that season on injured reserve.
ESPN's Jeremy Fowler and Sarah Barshop contributed to this report.