These days, the legal marijuana industry receives most of the attention. But according to a new report by Arcview Market Research, black market marijuana sales made up 87 percent of all pot sales across North America in 2016.

The report, which will be released in full in February, found that legal marijuana sales reached $6.9 billion across the U.S. and Canada, growing by a whopping 34 percent compared to the year before. And yet, despite the fact that eight states and Washington, D.C. legalized adult-use marijuana, and 28 states approved medical marijuana programs, the black market still managed to capture $46.4 billion in sales.

To compile the report, Arcview gathered data from BDS Analytics, a market intelligence firm that tracks millions of legal transactions from cannabis dispensary point-of-sale systems. Combined sales--both legal and illegal--in the industry totaled $53.3 billion, which is a pretty astounding figure. (To provide some context, wine sales reached $38 billion in 2016.)

Troy Dayton, CEO of Arcview Market Research, says that the true opportunity of legalization lies in the prospect of transforming all of the demand and economic activity in the black market into regulated, legal consumer spending in the legitimate economy. Instead of spending money on enforcement, states can make money by collecting taxes. Entrepreneurs, unlike other industries, know that an industry starved for legitimate retail and consumer experiences is waiting in the black market.

"The enormous amount of existing, if illicit, consumer spending sets cannabis apart from most other major consumer-market investment opportunities throughout history," Dayton said in a statement. "[The] cannabis industry doesn't need to create demand for a new product or innovation--it just needs to move demand for an already widely-popular product into legal channels."

The report also found that black market sales in North America decreased by 3 percent from 2015 to 2016, a sign, although small, that legal markets have taken a bite out of black market marijuana.

As for the expansion of the legal market, sales are projected to grow at a compound year-to-year growth rate of 26 percent for the next four years. By 2021, the legal industry is expected to reach $21.6 billion.

The black market will atrophy as more states legalize and open state-regulated marijuana markets, according to the report. By 2021, the black market is estimated to shrink to 67 percent of the total market in North America.