Gibson, a guard-center, was a 2008 sixth-round draft pick of the Eagles before spending parts of the last three seasons with the Seattle Seahawks. He appeared in Seattle's final three games during the 2011 season after playing in 14 games, including eight starts, the prior season.
Vallos, a center-guard, was a 2007 draft choice of the Seahawks and spent the entire 2007 season on the team's practice squad. He spent the last four seasons with the Seahawks (2008-09) and the Cleveland Browns (2010-11), appearing in 40 contests, including eight starts.
The Eagles solidified their offensive line on Saturday, when the team agreed to a five-year, $27 million deal with guard Evan Mathis.