Mike Gundy believes his mullet is worth millions.  

The Oklahoma State coach, who turns 50 next month, says he often wonders about the value of his throwback hairstyle that started as a joke last summer. 

(Oklahoma State head football coach Mike Gundy after speaking to reporters during the Big 12 football media days in Frisco, Texas. AP Photo/LM Otero)

Gundy says that would be good research for some marketing majors to do, but he figures the dollar amount is "somwehere in the millions for the amount of time that we've had on the air for that."

While he recently got a new five-year contract worth more than $20 million for his work as coach, Gundy says maybe he should get an extension and raise for all the free marketing for Oklahoma State because of his hair. 

There was 3 1/2 minutes on ESPN earlier this year _ that's free airtime _ in a segment with NHL commentator and fellow mullet-wearing Barry Melrose. There are Oklahoma State T-shirt with the mullet, which has also been featured in other marketing and social media campaigns.

It all started after Gundy's youngest son noticed his dad's hair getting a little long last summer. The boy joked about him letting it grow out.

And it has _ even with a recent trim because it was getting "ponytail potential." Gundy's hairstyle is now similar to what he had in the late 1980s when playing quarterback for Oklahoma State.