The Buffalo Bills had their best season in a decade, but they find themselves in search of a new head coach. Doug Marrone surprised many when he opted out of his contract, and now the organization must replace their coach of two years.

Black Monday brought about five head coaching vacancies, and the Bills are in competition with other teams, who are interviewing many of the same candidates as Buffalo. Marrone appears to be the favorite to be hired by the New York Jets, but since Jim Harbaugh signed a contract to become Michigan’s next head coach, there is no one clear-cut candidate that stands out among the rest.

Buffalo is doing their due diligence, contacting teams around the league about the opportunity to interview their assistant coaches. Josh McDaniels, Hue Jackson and Darrell Bevell are among the many coaches that the Bills are considering.  

Below are five candidates who appear as the most likely hires for Buffalo.

Mike Shanahan

Shanahan is the most accomplished of all the potential candidates, and ESPN’s Adam Schefter reports that the two sides have spoken to schedule an interview. From 1995-2008, Shanahan reached the playoffs seven times with the Denver Broncos, winning two Super Bowls. However, he wasn’t nearly as successful with the Washington Redskins from 2010-2013, making the playoffs once and finishing with a 24-40 overall record. Shanahan spent 2014 out of football, and will be 63 years old at the start of next season.

Teryl Austin

He’s never been an NFL head coach, but Austin might soon get his chance. He’s drawn interest from multiple teams, including the Bills. The Detroit Lions defensive coordinator has plenty of time to interview, now that the team has been eliminated from the playoffs. Austin led the No.2 defense in the regular season, which held opponents to 17.6 points per game. He got his first NFL assistant coaching job in 2003, and reached the Super Bowl at his first three stops. Austin, though, has been a coordinator for just one season.

Frank Reich

The San Diego Chargers offensive coordinator appears to be high on Buffalo’s list of candidates. The 53-year-old first became an NFL assistant in 2008 when he joined the Indianapolis Colts’ staff, and he’s spent one season as a coordinator. Reich could also be New York’s top choice, if they don’t go with Marrone.

Dan Quinn

Quinn has already met with multiple teams about their head coaching vacancies, and he could be ready to get his first head coaching job. As the defensive coordinator of the Seattle Seahawks, he’s well thought of around the league, leading the NFL’s top defense in back-to-back seasons.  However, he might not be able to accept a job until February, as Seattle looks to win its second straight Super Bowl.

Adam Gase

After Marrone left Buffalo, Gase was the first name to be reported as his possible replacement. Gase is just 36 years old, but he’s been an NFL assistant coach for a decade, and the Denver Broncos offensive coordinator for the last two seasons. Even though he’s never been a head coach, Gase might not choose to accept a Bills offer. Last year, he declined the chance to be interviewed for the Cleveland Browns’ head coaching position. Gase remains a top candidate for the Bears, 49ers, and Falcons openings.