The Buffalo Bills have agreed with running back Frank Gore on a one-year, $2 million deal, a source told ESPN's Adam Schefter.

Gore is the NFL's oldest running back -- he will be 36 when the 2019 season starts -- but he showed little sign of being done in 2018. He joins a Bills backfield fronted by 30-year-old running back LeSean McCoy.

A five-time Pro Bowl selection, Gore is NFL's active career rushing leader with 14,748 yards for the San Francisco 49ers, Indianapolis Colts and Miami Dolphins. He's No. 4 on the all-time list, trailing only Barry Sanders, Walter Payton and Emmitt Smith, who are all in the Pro Football Hall of Fame. Gore needs just 252 rushing yards to reach the 15,000-yard milestone and 522 to pass Sanders to move into third place.

It is initially unclear where Gore fits into an experienced Bills backfield. Buffalo will now have the NFL's three oldest running backs -- Gore, Chris Ivory (30) and McCoy -- under contract for 2019. McCoy and Ivory both enter the final seasons of their contracts with salary-cap numbers of $9.1 million and $2.9 million, respectively.

Bills general manager Brandon Beane reiterated at the end of last season that McCoy was part of the team's plans in 2019, despite the six-time Pro Bowler having posted career lows in rushing yards (514) and yards per rush (3.2) last season. Ivory, whom the Bills signed as a free agent last offseason, rushed 115 times for 385 yards and one touchdown.

In 14 games last season, Gore led Miami with 722 rushing yards and an average of 4.6 yards per carry. He also had 12 receptions for 124 yards and a touchdown. He overtook Kenyan Drake to become the Dolphins' starter, and he quickly became one of the team's leaders.

Gore signed a one-year contract with the Dolphins last March to play in his hometown, where he starred in college at the University of Miami. He said earlier this offseason that he would have loved to finish his career in Miami.

Gore is one of the NFL's iron men. His 2018 season ended on Dec. 16 after he suffered a right foot sprain, which snapped a streak of 126 consecutive games that dated back to 2010.

The injury, which didn't require surgery, also snapped Gore's streak of 12 consecutive seasons with at least 1,000 total yards. But he has made a career of overcoming injuries, including two torn ACLs, two shoulder surgeries, a fractured hip and a broken hand.

In 2016, Gore became the first running back age 33 or older in more than 30 years to rush for 1,000 yards in a season. In 2018, he passed Payton and Smith for the most consecutive seasons (14) with 500-plus rushing yards.

ESPN's Cameron Wolfe and Mike Rodak contributed to this report.