Strategic Economics

Dark Pools, Internalization, and Where Order Flow Goes

Most orders never reach a public exchange. They are matched invisibly, or filled by a firm that bought the right to fill them, and the reason is the theory from the previous lessons: an order that carries no information is cheap to fill and therefore worth paying for. Learn who receives that value, and how to read the disclosure that tells you.

  • Advanced
  • 14 min total
  • 14 chapters

What decision this helps you make: Where to send an order and how to verify that the routing served you rather than whoever was paid for it. And, if you are the one routing other people's orders, how to make that decision defensible rather than merely disclosed.

What this topic is

A dark pool is a trading venue that accepts orders without displaying them, matching buyers and sellers invisibly, usually at the midpoint of the public quote, so that large orders can trade without announcing themselves. Internalisation is different and larger: a broker, or a wholesaling firm the broker sends orders to, fills a customer order against its own book instead of routing it to an exchange. In the United States, wholesalers commonly pay brokers for the right to receive that flow, an arrangement called payment for order flow. Together, these off-exchange channels handle a very large share of all trading, and almost none of it is visible while it happens.

Why it matters

This is where the three preceding lessons cash out. The spread exists because some counterparties are informed; retail orders mostly are not; therefore retail flow is cheaper to fill than anonymous flow, and something that is cheaper to serve will be competed for. Everything else follows from that one sentence: the payments, the price improvement, the segmentation of the lit book, the regulatory argument. Understanding it tells you why your zero-commission trade is not free, why institutional traders hide, what a routing disclosure is really telling you, and why a market can be simultaneously cheaper for individuals and worse at discovering prices.

Who should learn it

Investors who want to know what happens to their orders, anyone who routes orders on behalf of others and owes them a duty, founders and operators studying a business built on selling access to a customer base, and readers who want the concrete institutional version of adverse selection rather than the model.

What you will understand

  • Why an uninformed order is a valuable asset, and how the value gets split between customer, broker and wholesaler
  • How segmenting flow raises the informed share of everything left behind, with the arithmetic
  • How to read a Rule 606 order-routing disclosure and what to ask about each line
  • The genuine case for internalisation, and where the evidence on dark trading and price discovery actually lands

Prerequisites

Common misconception

"Zero commission means the trade is free, and dark venues are shady by definition." Both halves mislead. A zero-commission trade is paid for by the value of the order itself. The flow is worth money because it is uninformed, and the arrangement splits that value three ways, with a real share often going to the customer as price improvement. And a dark venue is not sinister; it is a response to the arithmetic of the previous lesson, where displaying a large order is what causes the impact you are trying to avoid. The serious questions are not about darkness or free trades. They are about who verifies the split, and what the segmentation does to everyone left on the lit book.