The boom around sports betting stocks is only heating up.

To date, we can bet on sports in Colorado, Illinois, Indiana, Iowa, Michigan, New Hampshire, New Jersey, Pennsylvania, Tennessee, Virginia, and West Virginia. Maryland is moving closer to legalizing sports gambling, with Governor Larry Hogan signing a bill that creates a framework for the industry. New York Governor Cuomo signed legislation that includes a framework for sports betting.

From here, if more states legalize sports gambling, the industry could be worth up $100 billion by 2023, according to Statista, as highlighted by Roundhill Investments. Analysts at “Macquarie believes online sports betting will be available to 96% of the U.S. population by 2025,” they added.

In short, we could be looking at monster growth here.

So it just makes sense to invest in some of the top online sports betting stocks, including:

• Penn National Gaming (NASDAQ:PENN)
• DraftKings Inc. (NASDAQ:DKNG)
• Roundhill Sports Betting & iGaming ETF (NYSEARCA:BETZ)
• VanEck Vectors Gaming ETF (NASDAQ:BJK)

Sports Betting Stocks: Penn National Gaming (PENN)

The last time I weighed in on Penn National Gaming, I said, “The pullback is temporary. With casinos reopening, and with PENN’s online sports betting app, I could see the stock back to $133 easily. I’d use the pullback as a buying opportunity.”

That was on May 13, as the PENN stock traded at $75.

Now, the company, which owns part of Barstool Sportsbook, has seen its stock go as high as $85.37 since that note before dropping a bit further down. Still oversold, I’d like to see PENN back above $100, near-term. Not only are casinos seeing far more foot traffic, but PENN is seeing a good deal of success with its Sportsbook.

So much so, PENN President and CEO Jay Snowden said, as quoted by SBC Americas, “Since launching our product just over seven months ago, we have registered more than 400,000 customers and generated over $660m and $61m in handle and gaming revenue, respectively. We plan for the online Barstool Sportsbook to be live in eight states by football season and in at least 10 states before the end of the year.”

Additionally, the company just launched its Barstool Sportsbook App in Indiana, with more states to come. So again, I’d use any weakness in PENN as a buying opportunity, especially in a market that could grow to $100 billion in the next few years.

Draftkings (DKNG)

The first time I weighed in on Draftkings, I said, “At $52.72, DKNG is still cheap, and could at least double from here on explosive catalysts.” That was on Sept. 21, 2020.

DKNG got up to a high of $74.38 by March and then fell apart.

However, don’t count the stock out just yet. With the sports gambling boom just getting underway, DKNG could be one of the top winners. For one, Goldman Sachs analyst Stephen Grambling upgraded the stock to a “buy” with a target of $87, as noted by Street Insider.

For two, according to Jason Park, DraftKings’ chief financial officer, “Our $312 million in first quarter revenue, 114% increase in MUPs and 48% growth in ARPMUP reflect solid customer acquisition and retention as well as successful launches of mobile sports betting and iGaming in new states. We are raising our revenue outlook for 2021 due to the outperformance of our core business in the first quarter and our expectation for continued healthy growth.”

While the DKNG chart has seen better days, I’d use weakness as an opportunity.

Sports Betting Stocks: Roundhill Sports Betting and iGaming ETF (BETZ)

One of my favorite ways to diversify is with an exchange-traded fund (ETF). Not only can I gain more exposure to dozens of hot stocks, but I can do so at far less cost.

Look at the Roundhill Sports Betting and iGaming ETF, for example. It includes both of the stocks I’ve discussed so far and several other notable names. After exploding from a 2020 low of $14.23, it opened on June 2 at $31.83.

If it can now break above resistance at $33.08, I’d like to see it closer to $45, especially as its top holdings take off. Draftkings, Penn National Gaming, Flutter Entertainment (OTCMKTS:PDYPY) and Scientific Games Corp. (NASDAQ:SGMS) are among the fund’s 41 holdings.

The expense ratio on BETZ is 0.75%, or $75 per $10,000 invested annually.

Van Eck Vectors Gaming ETF (BJK)

The world of sports betting stocks is large and diverse enough to support multiple ETFs that are worth our consideration. Which ETF you should invest in depends on how you feel about its combination of holdings.

We can also diversify well with the Van Eck Vectors Gaming ETF. After bottoming out in early 2020 at $20.02, the ETF opened at $55.44 on June 2. It has seen significant growth this year, but it might be able to go further.

If it can break above prior resistance at around $57.16, I’d like to see it closer to $65 a share as its holdings heat up. Some of its top holdings include Las Vegas Sands (NYSE:LVS), Caesars Entertainment (NASDAQ:CZR), Draftkings, Flutter Entertainment, MGM Resorts (NYSE:MGM), and Wynn Resorts (NASDAQ:WYNN).

The net expense ratio for BJK is 0.65%.

On the date of publication, Ian Cooper did not have (either directly or indirectly) any positions in the securities mentioned in this article. The opinions expressed in this article are those of the writer, subject to the InvestorPlace.com Publishing Guidelines.

Ian Cooper, a contributor to InvestorPlace.com, has been analyzing stocks and options for web-based advisories since 1999.