NEW YORK (Reuters) – The U.S. Securities and Exchange Commission is launching a review of the main set of rules governing stock trading, opening the door to the biggest potential changes in a decade-and-a-half, the head of the agency said on Friday.

The possible changes are aimed at making it easier to trade illiquid stocks, making more trading information available to investors, and improving the speed and quality of public data feeds needed for trading.

The SEC in 2005 adopted a broad framework called Regulation National Market System that was largely aimed at ensuring retail investors get the best price possible and preventing trades from being executed at prices that are inferior to bids and offers displayed on other trading venues.

Since then, faster, more sophisticated technology has put a bigger focus on rapid-fire, high-speed trading. There has also been an influx of new electronic stock exchanges, fragmenting liquidity and increasing costs for brokers around exchange connectivity and market data needed to fuel algorithmic trading.

“It is clear that the market challenges we faced in the early 2000s are not the same as the issues that we confront over a decade later,” Jay Clayton, chairman of the SEC, said at an event in New York.

To get a better grasp of current market issues, the SEC held a series of roundtable discussions with industry experts last year that led to potential rule-making recommendations around thinly-traded securities, combating retail fraud, and market data and market access, Clayton said.

Some areas the SEC is looking at include:

– Increasing the speed of, and adding more stock price information to, public data feeds to help make them more competitive against the more expensive, private data feeds sold by most stock exchanges.

– Allowing thinly-traded securities to trade only on their listing market, rather than on all 13 U.S. stock exchanges.

– Improving disclosure around reverse mergers.

– Adjusting the quote size of some high-priced stocks.

The 2019 review follows an active 2018 for the SEC.

The regulator adopted rules to increase transparency around broker-dealer stock order routing and private off-exchange trading venues. It also ordered a pilot program to test banning lucrative rebate payments that exchanges make to brokers for liquidity-adding stock orders.