Panellists warned the U.S Securities and Exchange Commission that changes to Rule 611, or the trade-through rule, could potentially harm the quality of the NBBO.

The National Best Bid and Offer is a composite of the highest bid and lowest offer across all U.S. equity exchanges in real time, and is used as a benchmark for best execution. The SEC hosted a roundtable for the investor advisory committee on 10 September 2026 in Washington D.C. The panel discussed Regulation National Market System (NMS) which has governed market structure for U.S. equity trading since 2006.

The regulator has proposed rescinding Rule 611, which was designed to ensure that investors receive  the best publicly displayed price regardless of which exchange executes their trade. The rule prevents trading venues from executing an order at a price that is worse than the best publicly displayed price on any other competing exchange.

Hubert De Jesus, global head of electronic trading and market structure at BlackRock, said on the panel that U.S. equity markets function exceedingly well for investors. He highlighted that average daily value traded in 2001 was $86bn and has risen to $824bn in 2025. Before 2001 trading costs were in excess of 100 basis points and have reduced to between 20 to 25 basis points for the same trade.

“This suggests that markets are not in need of wholesale change, and we do have to be very careful with regulation,” added De Jesus. “If the NBBO is the benchmark and that deteriorates, execution quality also deteriorates and the cost to get in and out of positions increases.”

BlackRock is also concerned that if Rule 611 is repealed, retail clients will occasionally be traded through and they will not get their execution price.

Jeff Mahoney, general counsel at the Council of Institutional Investors (CII), said on the panel that the not-for-profit, nonpartisan association of U.S. public, corporate, and union employee benefit funds opposes rescinding Rule 611. The association’s members have approximately $5.6 trillion in assets under management.

Mahoney said: “We share the concern of many commentators that the commission’s proposal to rescind the order protection rule constitutes a pretty big overhaul of our current equity market structure. We’re concerned that the overhaul may be inconsistent with current CII membership-approved policies relating to best practices of beneficial ownership as well as trading issues.”

As a result the Council of Institutional Investors believes Rule 611 should not be rescinded as proposed without more evidence that the cost savings from implementing this proposal will exceed the increased costs to investors, including the increased costs of failing to obtain best execution from their agent brokers. Mahoney claimed that agent brokers are often subject to significant conflicts of interest, including incentives to route for rebate payments rather than to markets that provide the best overall outcome for  investors.

The Council of Institutional Investors is also worried about the impact of rescinding Rule 611 on retail investors.

“The SEC found in its 2005 rule making that Rule 611 was saving American retail investors billions of dollars every year,” Mahoney added. “If we eliminate Rule 611 that pricing efficiency will go away and it will be borne by retail investors.”

Panellist Adam Nunes, head of risk at market maker Hudson River Trading, said: “A few common themes have come out of this process and one is the critical importance of the NBBO as that stands today as a high quality piece of data. We want to make sure that that stays strong.”

However, Hudson River Trading believes that the trade-offs of rescinding Rule 611 will be positive and enhance competition and innovation.

Jim Angel, associate professor at Georgetown University, argued on the panel that removing the trade-through rule will not necessarily harm the NBBO as the best execution requirement will remain and it is in brokers’ self-interest to want to trade at the best possible price for their clients.

Angel agreed that having a best bid and offer is a very important benchmark, but that the current NBBO is obsolete because it is based on round lots, while half of trades now take place in odd lots.

“So the NBBO is not really a good representation of what is out there in the market,” added Angel. “We should measure best execution on a trade-by-trade basis with respect to the actual displayed liquidity in the market, which would give us an effective best bid and offer.”

He recommended that whether or not Rule 611 is repealed, the SEC should rethink how the NBBO is calculated.

Chuck Mack, head of strategic operations and public policy at Nasdaq agreed on the panel that U.S. equities markets are the cheapest place to trade relative to the rest of the world in terms of both commissions and  implementation shortfall, how much the market moves when traders buy or sell into the market, even though it is the most fragmented. There are currently 18 equities in the U.S. as well as over 30 registered ATSs and countless other single dealer platforms.

Mack also highlighted that dark trading, or trading off-exchange, is about 50% of total volume per day. In addition, even on an exchange another 20% of total volume is traded via non-display functionality and order types, so approximately 70% of the market is less transparent.

“We haven’t seen the displayed quote falling apart, which is a good thing, but there may be some tipping point at which that does happen,” said Mack.

He recommended that as well as reviewing Rule 611, the SEC should reconsider the different rules covering exchanges, alternative trading systems (ATSs) and rules for venues that are set by FINRA.

SIP data

The panellists also agreed that regardless of whether Rule 611 is rescinded, the SEC should consider how SIP market data revenue is distributed. All exchanges currently report their best bid, offer, and all trades to a centralized system that distributes the data for a fee. The collected revenue, hundreds of millions of dollars, is shared among the exchanges after expenses, based on a formula from FINRA.

Nunes said: “There is a pool of money that could act as a reward for certain behavior.”

De Jesus argued that the SIP consolidated data fee is a bigger contributor to the fragmentation in the market than Rule 611.

“Some small exchanges earn revenue and are not super-active in the market,” said  De Jesus. “A lot of that revenue also trickles back to other off-exchange platforms so it contributes to fragmentation in multiple places.”

The World Federation of Exchanges has also responded to the SEC’s consultation on the review of the trade-through rule and said its removal should not be viewed as a simple deregulatory measure. The WFE agreed that the merits of rescinding Rule 611 should not be considered in isolation.

“The case for removing the trade-through rule is compelling only if accompanied by a broader review of the regulatory framework,” added WFE.

SIFMA, a trade body for the U.S. securities industry, also said in a statement that it is important to identify and analyze interconnected market structure elements and study what corresponding impacts could stem from any intentional change, as well as the cumulative net effect of changes.

“This is particularly true today, as the landscape for modern securities markets is under consideration in conjunction with extending trading into overnight hours and the incorporation of tokenized securities,” said SIFMA.