Just over a year ago, the Supreme Court opened the door to states all over the country to allow sports betting, and there's now a rush of companies trying to position themselves to win the market. Casino companies are building partnerships to supply as many states as possible with the physical locations and apps to reach as many bettors as they can. Whoever can reach the most will win a prize that could be worth billions for casino stocks

Here's a look at how the landscape is shaping up and what to watch for in sports betting over the next decade. 

Sports betting tickets on a table with cash.

Image source: Getty Images.

Caesars' early move into sports betting

Caesars Entertainment (NASDAQ:CZR) partnered with DraftKings to get into sports betting early. It's already running sports betting in seven states, with mobile sports betting in Nevada, New Jersey, and -- later this year -- Pennsylvania. 

The merger with Eldorado Resorts (NASDAQ:ERI) would expand the company's footprint and give it a larger network of potential customers. There's a reason that scale is something casino companies are trying to build. 

MGM builds a wide betting network

Not only does MGM Resorts (NYSE:MGM) have one of the biggest networks of casinos in the country, it's also building a valuable set of distribution partnerships. The company's recent deal with Buffalo Wild Wings will bring sports-betting odds to locations where bets aren't even legal yet. Where they are legal, the company will provide the mobile platform for betting. 

MGM has also partnered with the NBA, WNBA, NHL, and MLS. Caesars got the NFL deal, but MGM is clearly leading in league partnerships, and that may be enough to make it a go-to for gamblers. 

The supplier side

International Game Technology (NYSE:IGT) isn't going to be the face of sports betting in the U.S., but it'll be a key service provider for some casinos. The company's PlaySports platform will be powering sports betting at Resorts World Catskills and betting destination Sportsbook 360. 

The company's platform is now available in eight states. It will be a key way for smaller casinos to take bets and compete with the large casino networks. 

The regional player's guide to sports gambling

Penn National (NASDAQ:PENN) is taking a broad approach to the market with a number of brands. Kambi is the company's technology supplier that will build everything from the front-end user interface that bettors see in mobile apps, to the odds-compiling and risk management that Penn National will use to make money. 

In some unique partnerships, the casino license Penn National owns will be used by DraftKings, PointsBet, theScore, and The Stars Group (NASDAQ:TSG) for their gambling offerings. Each will use "skins" to brand their own sites sites or apps but Penn National will be the casino taking the bets. Think of it like "skins" that used to be common on smartphones, making them look different even though the underlying product was the same. Operationally, skins essentially allows Penn National's license to be sold on multiple platforms that ultimately feed back to one license, which is leverage in reaching new customers. 

It's not clear if the casino brand or the online poker/betting brand will be more powerful to mobile sports betting, but Penn National is taking the approach of partnering with multiple brands and hoping that one of them wins. 

The prize for sports betting winners

The exact size of the sports betting market is uncertain, since there are only a few states where it's legal. But the opportunity is worth billions in the long term for casinos that can gain market share. You can see multiple strategies being deployed, so investors should watch for what one wins, because there's a huge upside for the winners.