Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you'd like to add some gambling stocks to your portfolio but don't have the time or expertise to hand-pick a few, the Market Vectors Gaming ETF (NYSEMKT:BJK) could save you a lot of trouble. Instead of trying to figure out which gambling stocks will perform best, you can use this ETF to invest in lots of them simultaneously. (Note that the industry uses the term "gaming," but it's hard not to see it as gambling when customers are risking, and losing, a lot of money.)

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. This ETF, focused on gambling stocks, sports a relatively low expense ratio -- an annual fee -- of 0.65%. The fund is fairly small, too, so if you're thinking of buying, beware of possibly large spreads between its bid and ask prices. Consider using a limit order if you want to buy in.

This gambling-stocks ETF has outperformed the world market over the past three and five years. As with most investments, of course, we can't expect outstanding performances in every quarter or year. Investors with conviction need to wait for their holdings to deliver.

Why gambling stocks?
Whether you approve or not, casinos and gambling seem to be here to stay, and the games they offer are designed to make gamblers lose, overall, while the house wins. Not all casino companies are the same, though, so you should choose carefully or invest in a big basket of gambling stocks via a fund such as the Market Vectors Gaming ETF. Gambling stocks have dropped in value lately, offering even better entry points for interested investors.

More than a handful of gambling stocks had strong performances over the past year. MGM Resorts International (NYSE:MGM) surged 93%. It has become the hottest company in Las Vegas, it's doing well in China (with fourth-quarter revenue there up 27%), and it's looking to expand in Japan. It also has a well-diversified revenue stream, generating most of its Las Vegas Strip revenue from lodging, food, and entertainment. In its fourth quarter, MGM Resorts International posted a 10% year-over-increase in revenue and $330 million in consolidated operating income, compared with a $425 million loss last year. Some wonder whether its debt burden will constrain its expansion plans.

Melco Crown Entertainment Ltd. (NASDAQ:MLCO) jumped 57% over the past 12 months. Many investors are excited about its new Studio City casino, occupying a prime position on the Cotai Strip of Macau. Its other projects include the City of Dreams Manila casino, opening in 2014 in the Philippines. It's a Macau pure play for now, offering possibly greater reward in exchange for greater risk.

Las Vegas Sands Corporation (NYSE:LVS) advanced 43% and is yielding 2.7%. The world's largest casino-operator (by revenue), Las Vegas Sands has been growing briskly, with five-year average annual growth rates of 25.7% and 50.9% for revenue and earnings, respectively. With a forward price-to-earnings (P/E) ratio of 17, it's appealingly priced, too. Las Vegas Sands has been tackling its debt and rewarding shareholders with dividend growth and stock buybacks.

All of the companies above operate in the immense and growing Macau market. Gambling revenue in Macau grew 40% in February, and the takes in more than six times the revenue of Las Vegas.) Business is expected to keep growing in Macau in part due to a growing transportation system as well as China's growing middle class.

Other gambling stocks didn't do quite as well over the last year, but could see their fortunes change in the coming years. International Game Technology Corporation (NYSE:IGT) sank 15%, and yields 3.2%. It has been struggling lately, and it recently announced a 7% workforce reduction. Its first quarter featured disappointing adjusted earnings, down 13% over year-ago levels. Revenue was up 2%, but management's outlook was anemic due to weakness in the casino industry's gambling revenue. The bright spot was its social-gaming segment, where revenue surged 57% thanks to IGT's acquisition of DoubleDown Interactive. It reports its second-quarter results on April 22.

The big picture
If you're interested in adding some gambling stocks to your portfolio, consider doing so via an ETF. A well-chosen ETF can grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.