The Vikings coaching staff and front office are in the process of fully evaluating their roster as they plan for the opening of free agency in March as well as April's NFL Draft. As General Manager Rick Spielman, head coach Leslie Frazier and their respective staffs put their heads together, the Access Vikings team is doing the same. We are in the middle of delivering snapshot evaluations of every position group. Today, we look at the defensive line.

DEFENSIVE LINE

Get excited: At this time last year, the Vikings were vowing to find ways to get Everson Griffen on the field more, hoping to take greater advantage of his rare blend of size, strength and quickness. A training camp experiment with Griffen at linebacker was quickly scrapped and defensive coordinator Alan Williams instead settled on a role that utilized Griffen as both an end and as an inside rusher in passing situations. Griffen finished the regular season with eight sacks, third on the team behind Jared Allen (12) and Brian Robison (8.5). Griffen also had an interception in Week 15 in St. Louis, returning that 29 yards for a touchdown. It was an eye-opening display of speed and athleticism for a guy who measures 6-foot-3, 273 pounds. He also had one of three Viking sacks of Aaron Rodgers in the Vikings' playoff loss in Green Bay.

Coach Leslie Frazier continues to laud Griffen's maturity and increased willingness to study the game. And Griffen's emergence will allow the Vikings some flexibility on the d-line as they put together their future plans.

Griffen is entering the final season of his rookie contract. And if his production continues escalating, you can bet General Manager Rick Spielman will try to find the right timing to lock Griffen up for the long-term well before he'd be able to become a free agent in March 2014.

Keep an eye on: Defensive tackles in this spring's draft. There's a belief that this year's draft class is stacked at that position, which may tempt Spielman to alter the 2012 interior rotation that featured Letroy Guion and Fred Evans at nose tackle and Kevin Williams and Christian Ballard at the under tackle spot.

On a draft analysis conference call Wednesday, ESPN expert Mel Kiper Jr. rattled off a handful of tackle prospects who might make sense for the Vikings. Say, for example, the team uses free agency to address its need for an outside receiver. Then it could possibly make sense to give Georgia's John Jenkins a long hard look with the No. 23 pick. Jenkins is 6- 3, 358 pounds and can be a fantastic plug in the middle of the defense.

But even if the Vikings wanted to wait to address their defensive tackle needs, they'll have decent options in later rounds. In the Round 3 range, for example, Kiper mentions Penn State's Jordan Hill as an option. He also offers a couple of sleepers for the fourth or fifth round in Missouri Southern State's Brandon Williams and Georgia Southern's Brent Russell.

There's also Bowling Green's Chris Jones, who will be cast aside by many teams as undersized. But Jones is a smart player with a high motor whom Kiper said was "as productive as any defensive tackle in college football this year. At any school, at any program."

Reason for worry: Age. Three of the Vikings' four d-line starters in 2012 will be in their 30s by the time training camp opens.

So now comes time to ask that difficult but necessary question: Just how much do the older guys have left in the tank? And might the Vikings ask either Jared Allen or Kevin Williams to restructure their contracts this offseason?

Allen will head to his fifth Pro Bowl in the last six seasons next week. But his inclusion in this year's game was based more on past reputation than this season's production. Allen played most of the year with a torn labrum in his left shoulder, an injury he will need surgery to fix following his trip to Honolulu. How fast he bounces back remains to be seen. Contract-wise, he's also entering the final year of his deal and will be owed in excess of $14 million in 2013. And it's far from a given that Allen, now nearing his 31st birthday, will remain with the organization beyond that.

Williams, meanwhile, will turn 33 in August. And while he's one of those ideal hard-working, low-maintenance leaders who fits Frazier's blueprint for success, the mileage of 10 full NFL seasons is catching up. Taking loyalty and emotion out of the equation initially, it'll be up to Spielman and his staff to deliver an honest assessment of just how much they think they can still squeeze out of Williams going forward. At present, Christian Ballard is in line to be Williams' successor. But Ballard hasn't yet established himself as a can't-miss fallback plan.

It wasn't long ago that Allen and Williams were dominant game changers whose presence was noticeable every Sunday. And to be clear, both are still very good players who can steady and energize the defense. But for how much longer? That's the type of question that the NFL's best teams have instinct for answering.