When the Gamecocks and the Tigers kick-off their football seasons this week, it will trigger the beginning of more than $120 million in combined economic activity from the seven home games each school has scheduled.

And locally, perhaps the simplest way to explain the economics of college football in South Carolina might be to look at the keg orders at Charleston’s King Street Grille.

During the slower summer months, the downtown sports bar says it needs only three or four kegs a week, plus an additional 20 cases of bottles and cans.

Yet when the football season starts, the numbers skyrocket, with demand hitting 15 or 20 kegs and 40 to 60 cases iced down and ready.

“People start coming in at 11 a.m. and they’ll be here until midnight,” Gerald Beattie, one of the general managers, said of football Saturdays. “And they are spending money the whole time.”

Heading into the 2013 season, experts who track college football economics say South Carolina is on the verge of its most profitable year ever in terms of a statewide financial windfall tied to football Saturdays.

With its two flagship schools ranked in the pre-season Top 10, South Carolina will be challenging perennial states like Florida and Alabama for dual-program profile, generating more alumni interest, drawing traveling fans from other schools and seeing an overall upswing in activity.

And that means millions of dollars are expected to be pumped into bars, eateries and fan stores from the mountains to the coast.

“It’s not like the state’s economy would not exist without college football,” said Robert T. Carey, director of the Economic Modeling Laboratory at Clemson University. “But it certainly would be a good bit smaller.”

University of South Carolina professor Tom Regan, of the school’s Department of Sports and Entertainment Management, added that things are going so well for USC that the school more than others is enjoying “the golden age of college football.”

“You’ve heard of the tax-free weekend?” he said. “This is like a tax-benefit holiday,” he said of the three days that are built around Saturday home games in Columbia that are book-ended by Friday and Sunday.

That’s especially true for the school since joining the Southeastern Conference in 1990, he said. “SEC football is the thing to do in Columbia and the Southeast,” Regan said.

While the total collective impact of all the elements of a college season on the state is an almost incalculable figure, USC and Clemson have done studies on what their football programs have meant in years past.

Clemson’s Carey reported last year that an average home football game accounts for: 198 jobs, $10.3 million in total output, $733,000 in net state revenue and $542,000 in net local government revenue.

Regan’s USC report last year said that for each game played in Columbia, it means at least $6 million will be spent — mostly in the Midlands — between Fridays and Sundays on hotels, food, drinks, tailgates and T-shirts.

Carey also studied The Citadel, estimating that the school’s football program creates about 158 jobs statewide per year, 136 of which are in Charleston County, with an estimated net impact on state government revenues of about $764,000.

While the numbers aren’t enough to threaten the coast as the top draw in the state’s $16.5 billion-a-year tourism industry, Carey, from Clemson, said college football essentially is its own form of tourist season.

That’s because football means people are moving around the state for games or going out to spend money and filling up places like the King Street Grille.

Reach Schuyler Kropf at 937-5551.