Central Limit Order Book

A central limit order book, often shortened to CLOB, is the peer-to-peer matching engine used by many prediction market exchanges. Participants post limit orders to buy or sell outcome shares at a chosen price, and the engine matches them by price-time priority so the keenest-priced and earliest orders fill first. Kalshi and Polymarket both operate this way, pairing traders against each other rather than against the house.

In this model the operator is not a counterparty to the trade. Instead it earns transaction fees on matched volume, which is a fundamentally different economic position than a sportsbook that books bets against a market-maker-broker and relies on a built-in margin. There is no house edge embedded in the price, because the price is set by the orders traders themselves submit.

A CLOB contrasts with an automated market maker, which always quotes a price from an algorithm, and with a parimutuel market, which pools all stakes and splits the pool among winners after the event. Order-book venues tend to give tighter spreads in active markets but can show thin depth when few traders are present, which is where dedicated liquidity providers help fill the book. Each model carries a different liquidity and fee profile for the operator.

For affiliate programs, the CLOB structure makes attribution clean because every matched trade is a discrete, fee-bearing event tied to an account. Operators can credit a referring partner on the fees produced by a trader's matched orders over time rather than on a single signup. This supports volume-based commission that mirrors how introducing-broker models work in trading venues.