Source: Logan Mankins has $20M bonus

The contract extension signed by New England Patriots offensive lineman Logan Mankins is worth $51 million over the next six years, and includes a $20 million signing bonus, according to a league source.

When looking at the six years of the deal, and Mankins' $8.5 million per year average, it makes him the highest-paid interior offensive lineman in the NFL.

Mankins will earn base salaries of $1.5 million in 2011; $3 million in 2012; $6 million in 2013; $6.5 million in 2014; $7 million in 2015 and $7 million in 2016, according to the source.

His contract includes $30 million guaranteed, sources told ESPN senior NFL analyst Chris Mortensen.

Mankins was designated the Patriots' franchise player in 2011 and was scheduled to earn $10.1 million this season. This deal pays him more than double that this year, while offering him the long-term security he desired.

It also provides the Patriots some salary-cap relief, with Mankins' cap number reduced from $10.1 million to about half of that figure.

Mike Reiss covers the Patriots for ESPNBoston.com.