7-Eleven is giving away free Slurpee's frozen drinks Monday in celebration of the convenience store chain's birthday. Reuters

Today is the day all hot and thirsty Slurpee aficionados have been waiting for -- it's free Slurpee day at 7-Eleven. All day Monday participating 7-Eleven stores nationwide are offering free 7.11 ounce Slurpee drinks to customers, in a promotion that continues until midnight.

Based in Dallas, Texas, 7-Eleven is America's largest convenience store, and the Slurpee, a sweet, flavored frozen beverage, is a signature product. 7-Eleven licensed Slurpee from the ICEE company in 1967, featuring the product in its stores.

ICEE is popular as well, with a Top Ten free app at Apple's iTunes store.

7-Eleven expects to give away more than 5 million free Slurpee's Monday, in celebration of the convenience store chain's birthday, on 7/11.

Based on the number of stores 7-Eleven, that's an average giveaway of roughly 1,000 Slurpee's per store expected. But don't feel sorry for 7-Eleven, the convenience store chain isn't getting clobbered on the promotion. Hardly. Last year when 7-Eleven did the free Slurpee promotion in a birthday celebration on 7/11 the company saw a sales increase of 38 percent.

With the free giveaway promotion, 7-Eleven actually had a heyday in sales -- its biggest of the year.

You get a taste of it, said Slurpee senior brand director Laura Gordon, and you choose to have more.

But it's more than that, since 7-Eleven sells much more than Slurpee's. People wanting to line up and wait for the free frozen drinks are buying more gas, more coffee, and more of other top-sellers at America's largest convenience store chain.

Slurpee fans can also visit the company's signature website, slurpee.com, downloading hats and confetti to join the celebration. They can even take a picture of themselves in celebration mode and post it on Slurpee's Facebook page.

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