24-Hour Market Trading Regulation Issues

And How Some Are Already Being Solved

The trading day no longer ends at 4:00 p.m. or even 8:00 p.m. ET. As liquidity builds overnight, U.S. equities increasingly require 24-hour market trading regulation, but oversight is still catching up.

Today’s market structure was built around a clearly defined core session, reinforced by frameworks like Regulation NMS. But these protections don’t automatically extend to alternative trading systems (ATSs) operating after-hours. While there are many benefits of these overnight venues, one issue is the gaps in transparency, oversight, and execution quality.

Now, with overnight venues like Blue Ocean ATS, MOON ATS, and Bruce ATS gaining traction, those gaps are becoming more consequential. The industry is responding. However, meeting the demands of a 24-hour market also requires more than new rules—it demands the right data.

In this piece, Exegy and BMLL team up to examine the state of 24-hour market trading regulation, what’s already changing, and why real-time and historical data are essential to future oversight.

What After-Hours Trading Regulatory Oversights Exist?

The design of U.S. equity market regulation is for a world with fixed hours. Regulation NMS was built around the core session of 9:30 a.m. to 4:00 p.m. ET when price discovery is deepest, and protections like the National Best Bid and Offer (NBBO) apply. But that structure doesn’t carry over into the extended or overnight sessions. Outside those core hours, key requirements around best execution, routing transparency, and quote display are either reduced or non-binding.

Alternative Trading Systems (ATSs) have stepped in to meet rising demand for off-hours liquidity. These venues allow broker-dealers and institutional clients to trade when traditional exchanges are closed. But they do so under a different set of rules. While ATSs must register and report volumes via Form ATS, they aren’t subject to the same quote dissemination and order protection obligations as exchanges during regular hours.

This lack of oversight creates both opportunity and risk. On one hand, overnight venues can quickly adapt to user needs and support broader participation. On the other hand, the absence of consolidated price signals and protections can make execution quality harder to evaluate. For broker-dealers, this means more responsibility for verifying best execution across fragmented venues and thinner liquidity. For regulators, it means fewer tools to monitor or enforce market behavior in real time.

As more trading migrates into new hours, these gaps become more material. The result isn’t just a regulatory lag—it’s an operational challenge for the firms navigating the shift.

What Changes Are Being Made for 24-Hour Market Trading Regulation?

The gap in oversight during off-hours hasn’t gone unnoticed. But instead of rushing to introduce sweeping new rules, regulators and market committees are taking a more practical, step-by-step approach. The focus right now is on expanding visibility and operational coverage because you can’t regulate what the market can’t consistently see.

One of the clearest signs of progress is the move to extend SIP operating hours. Both CTA/CQS and UTP have submitted a Plan Amendment to extend SIP hours to near-24-hour dissemination, with a one-hour technical pause each day, targeting Dec 2026 pending SEC approval.

This change isn’t just a technical tweak. Expanding SIP hours reflects a broader recognition— as trading extends into new hours, the need for shared quote and trade data becomes even more critical.

Exchanges are also pushing ahead through their own formal processes. We’re seeing a growing number of rule filings and initiatives aimed at enabling near-continuous weekday trading, not as flashy announcements, but as carefully structured shifts that must work across compliance, infrastructure, and participant workflows. Nasdaq, for example, has publicly signaled its intention to offer 23/5 trading (pending approval), while NYSE Arca has proposed extending to 22/5 (subject to approval), and Cboe has announced plans for 24/5 trading on EDGX (subject to regulatory review).

What all these efforts have in common is a shared understanding: as overnight trading becomes more routine, the absence of oversight isn’t just a gap; it’s a growing risk. The focus is no longer on whether these markets should exist, but on how to ensure they function with the same level of transparency and coordination as traditional hours. These changes, ranging from expanded SIP hours to exchange rule filings, are foundational for 24-hour market trading regulation.

What Is the Overnight BBO — and Why It Matters

Defining the Overnight Best Bid and Offer (OBBO)

The Overnight Best Bid and Offer (OBBO) is exactly what it sounds like: a consolidated reference for the best bid and best offer across all venues during the overnight trading session. Under today’s market data regime, the traditional National Best Bid and Offer (NBBO) only applies during core session hours, leaving a gap in standardized price discovery once the U.S. cash market formally closes. The OBBO closes that gap by creating a consistent best‑price reference that reflects activity outside normal hours — across regulated overnight venues and alternative trading venues that are increasingly active.

Why the OBBO Was Created

As liquidity and participation in off‑hours trading continue to grow — driven by global demand and retail engagement — the lack of a shared, consolidated price reference has become a real blind spot for both firms and regulators. An OBBO provides a common frame of reference for where the market is actually trading overnight, rather than letting each participant build their own fragmented view. This transparency matters not just for execution quality and risk management, but as a foundation for meaningful transparency and oversight as trading moves closer to a near‑continuous model.

How OBBO Supports 24-Hour Marketing Trading Regulation

The launch of the first OBBO by Exegy marks a tangible step in market infrastructure — one that supports broader transparency for overnight trading. By producing a consolidated best‑price signal for off‑hours activity, OBBO:

• Fills the transparency gap left by the traditional NBBO, which isn’t designed for extended‑hours sessions.
• Enables surveillance and benchmarking across a longer trading day by giving regulators and participants a consistent price reference.
• Acts as a structural precursor to further transparency initiatives because many oversight tools — from best execution monitoring to consolidated surveillance feeds — depend on a reliable, standardized source of price truth.

In this way, OBBO doesn’t just tell you where the market is overnight; it helps make overnight liquidity meaningful to the broader ecosystem, as market structure continues to evolve toward longer trading hours and greater global participation.

Why Historical + Real-Time Data Matters

Overnight trading is no longer a novelty session. It’s becoming a sustained part of U.S. equity market structure. To understand what that means in practice, we partnered with BMLL to complement Exegy’s real-time overnight market data with BMLL’s historical dataset. That way, we could look beyond anecdotes and quantify what’s changing, where liquidity is forming, and how market quality is trending across venues over time.

“Overnight markets continue to grow, with multiple venues competing for liquidity. To trade efficiently, participants need deep insight into historical venue liquidity and market quality, alongside access to high-quality real-time data to achieve best execution.”

– Eliott Banks, Chief Product Officer, BMLL

Real-time vs. Historical Data— What’s Its Purpose

Why Real-time Data?

Real-time data gives you a snapshot of what is happening right now, and is what makes overnight trading actionable. Liquidity can be thinner, faster-changing, and more venue-dependent than the core session—so participants need a live view to monitor conditions, validate execution outcomes, and adapt as prices and spreads move. That’s also why consolidated best-price reference points (Exegy’s OBBO) matter. It reduces guesswork and helps standardize where the market is outside regular hours.

What Historical Data Tells You?

Historical data is what helps firms identify trends and make operational decisions based on sustained data. It’s how you answer questions like: Is this growing structurally? Are spreads tightening over time? Is liquidity concentrating in predictable places? Is fragmentation emerging?

BMLL’s historical view supports the idea that this is not an edge-case activity. For example, their analysis estimates that roughly 11% of trading volume and 8% of notional occurs outside regular hours—evidence of an extended-hours footprint that’s already meaningful and measurable as a longer-term trend.

Figure 1 highlights how overnight liquidity behaves in core overnight sessions vs. regular hours

Closer Look at Fragmented Liquidity: Blue Ocean ATS

Blue Ocean ATS (BOATS) is an overnight ATS that enables trading in U.S. NMS stocks during after-hours trading. The venue is designed to overlap with the growing demand for APAC retail traders to conduct business during their daytime hours. The market utilizes clearing and settlement through NSCC/DTCC and regulatory reporting through FINRA venues, so participants can access overnight liquidity without reinventing their workflows.

Why Blue Ocean?

BOATS is the incumbent overnight venue. Throughout 2025, it had the highest amount of trade participation, which makes it the cleanest baseline for understanding how liquidity behaves when it moves outside the core session. In other words, using BMLL’s data, Blue Ocean gives us enough historical runway to separate one-offs from repeatable patterns. Additionally, it helps us see what starts to change as competition increases across multiple overnight ATSs.

What Historical Data Tells Us?

BMLL’s historical data set shows two signals that matter as overnight trading matures.

First, activity concentrates where you’d expect it to be with the most liquid names. In Blue Ocean’s overnight session, the top 25 symbols account for roughly two-thirds of notional volume, dominated by major ETFs and highly liquid single names. That concentration is important because it indicates overnight liquidity isn’t random; it’s forming in predictable places that firms can study, monitor, and plan around.

Figure 2 shows TSLA spreads tightening significantly, comparable to other venues during day trading

Second, market quality can improve meaningfully over time as the data shows spreads tightening significantly. In names like TSLA, spreads can look comparable to other venues during day trading in certain periods as evidence that overnight is not inherently “wide and inefficient,” but increasingly competitive in the right symbols.

In short, these insights are the value of historical data. It shows how market quality is trending, which becomes even more critical as the overnight ecosystem becomes more competitive and fragmented across multiple venues.

The Korea Effect: Adoption, Competition, and Early Fragmentation

A big accelerant has been Korea’s reopening of daytime U.S. stock trading (which maps to overnight hours in the U.S.). After the 2024 Blue Ocean incident, Korean brokerages resumed with stronger safeguards and expanded connectivity beyond a single venue. The Korea Times reports brokers signed agreements with Blue Ocean plus two additional ATSs—Bruce and MOON—as backups, effectively institutionalizing multi-venue access.

That lines up with what we’ve seen from MOON ATS activity: average daily notional activity rose 200%+ from early September through year-end, stepped up after Korea opened in November, and continued into early 2026 with new highs—supporting the view that overnight trading is becoming a sustained feature, not a seasonal one.

Figure 3 shows increased competition between the three overnight venues, leading to fragmentation

With multiple venues in play, competitive dynamics change. BMLL’s takeaway is that competition is increasing, and fragmentation is beginning to emerge across the three overnight venues, alongside liquidity behavior that diverges from the core session—exactly the kind of shift that makes consistent benchmarking harder without the right data foundation.

Conclusion: Closing the 24-Hour Market Trading Regulation Gap

As trading moves toward near‑continuous hours, global visibility hasn’t kept pace, creating a transparency gap. While the industry awaits formal oversight expansions from regulators and market committees, firms like BMLL, with their historical data, and Exegy, with its real‑time Overnight BBO (OBBO), are helping — so that participants aren’t left to build their own visibility solutions from scratch.

Historical data helps you commit. It reveals trend‑based behaviors that inform strategy. BMLL’s work shows that meaningful overnight participation already exists outside core hours, giving firms the confidence to plan and optimize rather than guess.

Together, Exegy’s real‑time infrastructure and BMLL’s historical depth help close today’s transparency gap, giving firms both the live view and the evidence base they need while 24-hour market trading regulation catches up.