The Securities and Exchange Commission is seeking public comment on the roles of investment advisors in the recommendation and sales of exchange-traded products (ETPs).

As part of a broader inquiry into these increasingly popular investments, the agency said it is interested in hearing about how market professionals sell ETPs, especially to retail investors, and on investors’ understanding of the nature and use of them.

“As new products are developed and their complexity grows, it is critical that we have broad public input to inform our evaluation of how they should be listed, traded and marketed to investors, especially retail investors,” SEC Chair Mary Jo White said in announcing the study Friday.

At the end of last year, there were 1,664 ETPs with a market cap of just over $2 trillion, according to the agency.

ETPs accounted for 16.7 percent of U.S. equity trading by share volume and 25.7 percent by dollar volume in 2014.

Among the many other issues surrounding ETPs the SEC is looking into are arbitrage mechanisms and market pricing, legal exemptions and other regulatory positions related to the trading of ETPs, and securities exchange listing standards for ETPs. 

The complete request for comment can be viewed at the SEC's website.

The agency will be officially taking comments for about 60 days. However, the SEC regularly accepts submissions after the official deadline.