Left tackle has been considered the most important position on the offensive line in the modern NFL because of the responsibility of protecting a quarterback's blind side in the passing game. It has also been the highest-paid offensive line position. These things aren't expected to change anytime soon.

However, a shift is beginning to occur in salaries for interior offensive linemen. The top of the offensive guard market has jumped ahead of the top of the center market on the offensive line financial totem pole. Kelechi Osemele redefined guard compensation during the offseason when the Raiders offered him a five-year, $58.5 million contract that was worth a maximum of $60 million through incentives. At signing, $25.4 million of Osemele's deal was fully guaranteed. Prior to Osemele, the top guard deal signed in the last couple of years was Mike Iupati's five-year, $40 million contract, which he received from the Cardinals as a free agent in 2015. That deal included $22.5 million in guarantees.

kelechi-osemele.jpg
Kelechi Osemele has proven he's worth his sticker price in Oakland. USATSI

Osemele is living up to his massive contract. He has helped turn an already good offensive line into arguably the league's second-best one behind the Cowboys. The 18 sacks allowed by Oakland were the fewest in the league this season. It's also the lowest total in franchise history since sacks became an official statistic in 1982. Osemele earned his first Pro Bowl berth and is a leading candidate for All-Pro honors.

The evolution of the interior linemen market

Centers started consistently eclipsing the $8 million per year mark in 2014. Alex Mack's five-year, $42 million contract with the Browns, which he could void after two years, made him the league's highest-paid center. Salaries for centers continued to escalate with Maurkice Pouncey, Rodney Hudson and Mike Pouncey signing deals averaging nearly $9 million per year with the Steelers, Raiders and Dolphins. Mack hit the $9 million per year market on a long-term deal with the Atlanta Falcons in March after opting out of his Browns contract. Travis Frederick's six-year, $54.6 million preseason extension with the Cowboys, containing slightly over $28 million in guarantees, is the current standard for centers.

Other guards are benefiting from effects of Osemele's contract. David DeCastro and Kyle Long received extensions averaging $10 million per year as the start of the regular season approached. Long's deal has $30 million in guarantees.

kyle-long.jpg
Kyle Long was the second-most athletic lineman in the 2013 NFL Draft. USATSI

Teams are placing more of a premium on athleticism at guard positions. This allows teams to better combat defensive tackles who can consistently pressure quarterbacks from the interior. The list of game-changing interior rushers includes the Bengals' Geno Atkins, the Eagles' Fletcher Cox, the Rams' Aaron Donald and the Buccaneers' Gerald McCoy. Edge rushers, such as Seattle's Michael Bennett, are also lining up inside on obvious passing downs so teams can generate a better pass rush.

Long, who spent time at guard and tackle in his lone season at Oregon, was arguably the second-most athletic offensive lineman at the 2013 NFL combine behind Terron Armstead. He was one of six offensive linemen to clock under five seconds in the 40-yard dash with a time of 4.94 seconds.

Graduating from college tackle to NFL guard

Some of the league's better young guards are converted college tackles. It isn't necessarily an easy transition after playing in space on the perimeter, particularly at left tackle.

Cowboys guard Zack Martin was a left tackle at Notre Dame. All-Pro Tyron Smith's presence at left tackle meant a position switch for Martin, which may have happened regardless of who drafted him because of concerns over his arm length.

Osemele was a left tackle at Iowa State. He spent his rookie season with the Ravens at right tackle before settling in at left guard. He moved back to left tackle down the stretch of the 2015 season with the Ravens when Eugene Monroe was lost to a shoulder injury. Cleveland's Joel Bitonio, who was a 2014 All-Rookie selection, played left tackle at Nevada.

Sometimes the position switch is done for a team to get its best offensive linemen on the field. Brandon Scherff, a left tackle at Iowa, was expected to be the Redskins' right tackle when he was drafted fifth overall in 2015. He was moved to right guard because of Morgan Moses' development. Scherff has quickly taken to his new position, earning a trip to the Pro Bowl this season. Laremy Tunsil, who dropped to the 13th overall pick in last year's draft after a video of him smoking marijuana surfaced, is beginning his NFL career at left guard for the Dolphins.

brandon-scherff.jpg
Brandon Scherff was a stud tackle in college who has turned into a Pro Bowl guard in the NFL. USATSI

The $10 million per year mark should become more of the norm for high-end guard compensation the next couple of years. The center market is more settled than the guard market, so a center earning $10 million per season may not be on the horizon in the immediate future.

T.J. Lang (Packers) and Kevin Zeitler (Bengals) are the impending free agent guards most likely to get deals comparable to those of DeCastro and Long. Justin Pugh could be in line for an extension with the Giants since 2017 is his contract year. He is scheduled to play 2017 on an $8.821 million fifth-year option. The second tier of guard salaries will likely hover at $8 million per year, where the market had been prior to Osemele's contract.

The next guard to set the salary bar

Martin is the best bet to set a new salary standard for guards. As a 2014 first-round pick, Martin is now eligible to sign an extension. If the timing of the deals of Cowboys center Travis Frederick and left tackle Tyron Smith, who were also first-round picks, are any indication, Martin's new deal will be in place before the 2017 season starts. Dallas made Frederick and Smith the highest-paid players (by average yearly salary) at their respective positions when they signed their deals. It's hard to imagine that Dallas won't do the same for Martin considering he is arguably the game's best guard, having earned three Pro Bowl selections in his three NFL seasons.

It remains to be seen whether the Cowboys stick with the league convention of left tackle sitting atop of the offensive line salary hierarchy, where Smith's $12.2 million per year average from his 2014 extension serves as a ceiling for Martin. Martin's overall guarantees should easily exceed Frederick's but may fall short of Smith's $40 million.

zack-martin.jpg
Zack Martin's next deal should reset the top of the market for elite guards. USATSI

Teams investing heavily in two guards is unlikely to occur since the salary cap forces teams to make choices on how to allocate financial resources. The Bears are currently the only team with two high-priced guards with Josh Sitton and Long. Sitton signed a three-year, $21 million deal after the Packers released him in preseason roster cutdowns. Martin's potential extension probably means impending free agent guard Ronald Leary won't be back with the Cowboys next season. He's done a good job filling in for 2015 undrafted free agent La'el Collins, who has missed most of the season with a right toe injury.

Once Dallas has three offensive linemen near of the top of their position markets, it's going to become increasingly difficult to have another high-priced lineman. It's conceivable that Leary could get a deal in the new second tier for guard salaries in free agency.