Dig into a college football coach's contract, and you'll find all sorts of interesting perks: car, phone and moving allowances. Country club memberships, paid by the university.

Even access to private jets for personal use.

In fact, according to USA TODAY Sports' annual review of coaches' compensation, at least 15 coaches who are at public schools have personal access to private jets written into their contracts this year – a stark uptick from a decade ago, when the perk was reserved for a handful of elite coaches.

Now, the free-flying group includes six Big Ten coaches, five in the Southeastern Conference and even one in the Group of Five: North Texas coach Seth Littrell.

Altogether, a dozen coaches' contracts grant them a combined 345 flight hours on private jets, while three coaches receive monetary allotments specifically for private jet use totaling $470,000.

Martin Greenberg, a Milwaukee-based sports attorney and adjunct professor at Marquette University, said these types of perks would have been "unheard of 20 years ago" but provide a tremendous – and somewhat hidden – value to coaches.

"When you look at the rankings of who gets what, even in (USA TODAY), there is no valuation given to these perquisites," Greenberg said. "This is one of the creative ways that agents can actually put more on the bottom line for their clients and keep their clients."

The Associated Press reported in 2017 that at least 20 public universities own or share ownership of private jets, with some employing full-time pilots.

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While several schools such as Arizona, Clemson, Minnesota and Purdue stipulate that their head coaches will be able to use private planes for recruiting or other trips related to their official duties, the perk of personal use is different. It essentially gives coaches access to private jets for family vacations or other leisure trips.

Some schools have offered this perk to their coaches for several years now. At Ohio State, for example, Jim Tressel and Urban Meyer both received more than 20 hours of personal flight time a year at various points. New coach Ryan Day, meanwhile, gets 50 flight hours — which is tied with Penn State coach James Franklin's annual allotment for the most personal flight time of any FBS public school coach.

Littrell, who is in his fourth season as coach of the Mean Green, negotiated for access to private aircraft in terms of dollars rather than hours when his contract was extended in May. He now receives $100,000 a year that is to be used specifically "to acquire private aircraft charter flight services."

"Coaches appreciate (this type of perk) because it makes their lives easy," Greenberg said. "Not only for themselves, but for their families."

Not every university has a private jet – and many simply aren't willing to include that perk in deals. But even so, there's plenty of room for creativity.

Mike Leach's contract with Washington State, for example, makes no mention of private jets, though it does mandate that the university upgrade Leach to first class, when available.

Contributing: Steve Berkowitz

Contact Tom Schad at tschad@usatoday.com or on Twitter @Tom_Schad.