The Buffalo Bills added a viable starting option to their quarterback roster Saturday night by reaching a contract agreement with free-agent Kevin Kolb.

The full terms of a two-year deal for the 28-year-old, five-year NFL veteran was approved by both sides about 9 p.m., a league source told The News.

The deal is expected to be worth a maximum value of about $13 million, which makes Kolb the clear favorite over incumbent seven-year veteran Tarvaris Jackson in the Bills’ QB competition. Jackson signed a one-year deal last month.

The Bills still are expected to take a quarterback in the NFL Draft and give the rookie a chance to win the starting job. However, with Kolb on board, the urgency to rush a rookie onto the field likely decreases.

Kolb’s physical talent and arm strength are comparable to that of former Bills quarterback Ryan Fitzpatrick. He is 9-12 as an NFL starter and has had some good moments on the field. He helped the Arizona Cardinals to a 4-0 start last season.

However, injuries have defined his career thus far. He played in only six games last season, getting knocked out for the year in Arizona’s Oct. 14 loss to Buffalo due to detached ribs and a sprained shoulder. Kolb suffered a serious concussion that caused him to miss the last three games of the 2011 season. He missed two games in the 2010 season due to a concussion, as well.

Kolb was released by the Cardinals earlier this month under circumstances similar to those that prompted Fitzpatrick’s departure from the Bills. Kolb was cut loose just before Arizona was due to pay him a $2 million bonus.

The Bills’ push to reach an agreement with Kolb came just as the NFL’s veteran QB market appears ready to dry up. Cleveland signed journeyman Jason Campbell earlier this week. Oakland reportedly is ready to release Carson Palmer in a salary-cap related move. The Raiders have an interest in Seattle backup Matt Flynn. The signing of Kolb leaves Flynn as arguably the last worthwhile QB acquisition available before the draft. A 2007 second-round pick of the Philadelphia Eagles, Kolb signed a five-year, $65 million contract with the Cardinals in July 2011, of which $12 million was guaranteed.

Overall, Kolb played in just 15 games with the Cardinals over two years, going 255 of 436 for 3,124 yards, 17 touchdowns and 11 interceptions. Playing behind a porous offensive line, he was sacked 57 times.

Jackson, who turns 30 in three weeks, owns a 17-17 record as a starter. Jackson was acquired by the Bills last August for a seventh-round draft pick. However, Jackson spent the entire season as the No. 3 QB in coach Chan Gailey’s offense. Jackson was re-signed by the Bills to a one-year contract in February.

The Bills also have 24-year-old Aaron Corp on the roster. Corp spent last year’s training camp with the Bills.