The Arena War

In Chapter 26, Larry Harris looks at the high-stakes competition between the marketplaces themselves. If you’re a developer building an ECN or a regulator at the SEC, this is the battlefield.

The Power of the Crowd: Order Flow Externality

The most powerful force in market structure is the Order Flow Externality.

• The Rule: Traders go where the other traders are.
• The Result: Liquidity attracts more liquidity. This makes it incredibly hard to start a new exchange. Why would anyone trade on “NewExchange” if there are no other buyers or sellers there?

This is a Network Externality, like a social media app. It doesn’t matter how good the tech is if none of your friends are on it.

Consolidated vs. Fragmented Markets

• Consolidated Market: Everyone trades in one giant room (like the Tokyo Stock Exchange).
  • Pro: It’s very easy to find the “best” price because all the orders are in one bucket.
  • Con: No innovation. If the exchange is slow or expensive, you have no other choice.
• Fragmented Market: Trading happens in many different places (like the US stock market today).
  • Pro: Intense competition. Exchanges and ECNs compete to offer the fastest tech and the lowest fees.
  • Con: “Search costs.” You have to check 15 different places to make sure you’re getting the best price.

Why Do Markets Fragment?

If the “Order Flow Externality” is so strong, why do we have so many exchanges? Because Traders are not all the same.

• The Whale: Needs a dark pool to hide a 500,000 share order.
• The Retail Joe: Needs a fast, $0 commission fill from a wholesaler.
• The HFT: Needs a high-speed API with 1-microsecond latency.

No single market can be perfect for everyone. This diversity of needs creates “niches” for new market centers to survive.

How Fragmented Markets “Coalesce”

Even though the market is split into many pieces, it acts like one big market thanks to three things:

1. Information Flow: Real-time data feeds let everyone see what’s happening everywhere.
2. Smart Routing: Computers (APIs) automatically check every exchange and send your order to the best one.
3. Arbitrageurs: If a stock is $10.00 on the NYSE and $10.05 on Nasdaq, an arbitrageur will immediately buy on the NYSE and sell on Nasdaq until the prices match.

The Public Policy Struggle

Regulators are always trying to find the balance.

• If they force everyone into one market, they kill innovation.
• If they allow too much fragmentation, it’s easier for brokers to “cheat” their clients in quiet, dark corners.

Summary: The Speed of Light

In the old days, regional exchanges (like the Philadelphia or Boston exchanges) survived because information moved slowly. Today, information moves at the speed of light. Consolidation is the natural state, and only the markets that offer truly unique services (like extreme speed or extreme confidentiality) can survive on the edges.

Next time, we’ll look at the ultimate battle of the 21st century: Floor vs. Automated Trading Systems.

Next Post: Floor Versus Automated Trading Systems