Sports betting is big business around the world, and it's been dominated for decades by traditional land-based casinos. That's changing as betting moves online, and the mobile gambling market took a major step forward in 2020 as more states legalized online gambling, and thousands of people began betting legally at home during the pandemic. A few companies hit public markets as well, bringing even more attention and funding to the industry. 

As we look back on the year and forward to 2021, the sports betting market has three clear winners in my eyes: DraftKings (NASDAQ:DKNG), MGM Resorts International (NYSE:MGM), and the little known GAN Limited (NASDAQ:GAN)

Two people betting on sports on a mobile device.

Image source: Getty Images.

DraftKings

The hottest sports betting stock of 2020 was DraftKings, hands down. The company hit the market through a special purpose acquisition company and hasn't looked back. Shares shot higher as the pandemic wore on and sports came back, helped by investors hoping that online betting would begin to replace in-person betting. For the year, shares are up 406%. 

In some ways, the boom in online betting is happening faster than expected, and that's helped early movers like DraftKings. In New Jersey, which is the bellwether for online gambling because it was the biggest early state to allow betting, there were $91.8 million in bets in November 2020 alone, up 86.9% from a year ago. If that growth and level of revenue are any indication of the potential for the rest of the country, DraftKings has a long runway ahead.

The third-quarter 2020 results were a small indication of how well things are going for DraftKings. Revenue was up 42% on a pro forma basis to $133 million, and monthly unique users grew 64% to 1 million. Revenue is also expected to be $750 million to $850 million in 2021, up 45% at its midpoint from 2020 guidance. This is a sports betting stock with a lot going for it and maybe just at the beginning of its growth story. 

MGM Resorts

As gambling moves online, companies with a physical presence can sometimes have an advantage over digital-only companies. They have known brands, regulators sometimes require a physical presence to operate in a state, and there can be synergies between real-world and online casinos. That's the space that MGM Resorts is trying to fill, and it's done so relatively well in 2020. 

The joint venture MGM Resorts built to enter the space is BetMGM, which is now offered in eight states and is growing as quickly as states will allow. Like DraftKings, the company is limited by what's legal in the U.S., but betting should be opening up in more states long term. 

What I like about MGM as a sports betting play is that it has a foundation as a physical casino company. MGM can use the cash flow from its casinos to fund online gambling development, and if it does that successfully it should add a lucrative business to the portfolio. 

GAN Limited

DraftKings and MGM are the companies that are taking bets and building the apps that consumers are using, but GAN is building the background infrastructure that online gambling is built on. Its software services include player identity validation, payment services, regulatory reporting, and even some game content. And with the recently announced acquisition of Coolbet, it'll enter the sports betting market worldwide.

If sports betting continues to grow, GAN will be one of the beneficiaries because it's providing services to multiple players. And I would expect some casinos and game companies that don't have the capital to build their own infrastructure to lean on a company like GAN. 

What's exciting about GAN is that it has the opportunity to grow with the online gambling and sports betting industries as well as grow the services it offers to clients. It already has a turnkey solution for infrastructure, but don't be surprised to see more games added to the portfolio so GAN can white-label the entire casino experience. That's where the real money will be made for this gambling stock. 

Online sports betting is booming

As more states are added to the legal betting industry, the amount bet on sports online is growing. And that's going to be a huge tailwind for DraftKings, MGM Resorts, and GAN Limited. The industry saw U.S. betting increase from $1.85 billion in August to $2.19 billion in September and is on its way to $3 billion in monthly bets. If the industry keeps growing at this rate, it could rival the revenue of physical casinos, and that would be a truly disruptive development in gambling.