Alternative Trading System (ATS) vs Stock Exchange: Key Differences

The table compares an alternative trading system and a stock exchange on what each is, who uses it, how it is regulated, tax, the main risk, liquidity and a typical example.

US law defines an exchange by what it does. Under SEC Rule 3b-16, a system is an exchange if it brings together orders from many buyers and sellers using fixed rules. By that test, most ATSs would count. Since 1998, Regulation ATS has given them a choice: register as an exchange, or register as a broker-dealer and follow Regulation ATS.

Most choose the second path. A system that complies with Regulation ATS is exempt from the definition of an exchange. The main duties are:

• Broker-dealer registrationThe operator registers as a broker-dealer and is supervised by FINRA, which publishes trading data for each ATS.
• Notice to the SECAn initial Form ATS at least 20 days before trading starts, and quarterly activity reports on Form ATS-R.
• Public disclosure for listed stocksAn ATS that trades listed stocks files Form ATS-N, which the SEC posts online once effective. The SEC adopted this form in July 2018.
• Fair accessOnce an ATS handles 5% or more of trading in a stock in four of the past six months, it must apply fair, written access rules.
• No “exchange” in the nameAn ATS may not call itself an exchange or a stock market.

The exemption has limits. If an ATS reaches 50% of trading in a security, or 40% in a class of securities, in three of four quarters, the SEC can require it to register as an exchange. It must first give notice.

An exchange carries heavier duties. It registers under Section 6 of the Exchange Act and acts as a self-regulatory organization, a body that writes and enforces rules for its members. It must file every proposed rule change with the SEC under Section 19(b). It also sets the listing standards that companies must meet.

A private company has no exchange listing, so its shares can only change hands privately. Some ATSs are built for these secondary transactions. The SEC’s list for September 30, 2026, includes Forge Markets, Hiive Markets and NPM Securities, among 81 systems.

An ATS gives buyers and sellers a place to meet. It does not remove the limits on private shares. The company’s transfer rules often require its approval and can give it the right to buy the shares first. Restricted shares also need an exemption to be resold, such as Rule 144. Each of these steps adds time before a trade settles.

Prices on these platforms are thin signals. A few trades can set a quoted price for a whole company. The broader market for such deals is covered in secondaries.

Alternative Trading System

For

Large orders can trade without moving the public price. Lighter rules let it serve niche markets, such as private shares and bonds.

Against

Less public price information. Trading can be thin. Access can be limited until an ATS reaches the 5% fair-access level.

Verdict: an ATS suits a trader who values discretion, or a holder of a security that no exchange lists. For private shares, it is often the only organized market, but it does not guarantee a buyer.

Stock Exchange

For

Public prices, deep liquidity in listed stocks and listing standards that companies must meet. The exchange polices its members.

Against

Only listed securities trade there. Large orders are visible and can move the price.

Verdict: an exchange is the default market for a listed stock and for most individual investors. Its rules, listing standards and published prices protect investors in ways an ATS does not have to. It has nothing to offer a company that has not listed.

For most individual investors, the choice is made by their broker. A broker decides where to send each order, and that can be an exchange or an ATS. You rarely pick one yourself.

For an employee or an early investor in a private company, the question is real. Before an IPO, an ATS may be one of the few ways to sell. Check the company’s transfer rules first, then the platform’s fees and how long settlement takes. After the IPO, your shares trade on the exchange once any IPO lock-up ends.

Buyers of private shares should expect less information than in a listed company. There is no prospectus and no daily price. The pre-IPO vs IPO guide explains what changes when a company lists.

Common Mistakes

• Thinking an ATS is unregulatedIts operator is a registered broker-dealer, and it files notices and reports with the SEC.
• Treating a platform price as the company’s valueA quote on a private-share ATS may rest on a handful of trades.
• Assuming a listing on a platform means you can sellThe company’s approval and securities rules still apply to private shares.
• Expecting a tax differenceThe venue does not change tax. What you sold and how long you held it does.

Alternative trading system (ATS)

A trading venue run by a broker-dealer that matches buyers and sellers without regulating them beyond their trading.

Stock exchange

A market registered with the SEC under Section 6 of the Exchange Act that lists companies and regulates its members.

Regulation ATS

The SEC rules, adopted in 1998, that let a trading system operate as a broker-dealer and avoid registering as an exchange.

Self-regulatory organization

A body, such as an exchange or FINRA, that writes and enforces rules for its members under SEC oversight.

Broker-dealer

A firm registered to buy and sell securities for customers or for itself.

Form ATS-N

The public disclosure an ATS that trades listed stocks files with the SEC about how it operates.

Fair access

The duty of a large ATS to admit participants under fair, written standards once it passes 5% of trading in a security.

FINRA

The self-regulatory organization that supervises US broker-dealers, including ATS operators.

Figures were last checked on October 29, 2026. The rules are United States federal rules. The ATS share of trading volume is the SEC’s figure from 2018 and has changed since.