Options accounts & routing
What is a Complex Order Book (COB) and how do institutional market makers fill multi-leg options spreads simultaneously?
By Easy Money Scanner · Educational reference · Not investment advice
The short answer
A Complex Order Book is an exchange's dedicated electronic matching system for multi-leg options strategies, allowing market makers and traders to post and match spread orders as a single unit rather than executing each leg independently against separate books.
How it works
Exchanges like Cboe aggregate complex order interest and run periodic auctions or continuous matching so multi-leg strategies like spreads, straddles, and condors fill simultaneously at one net price.
An example
An institutional trader submitting a 10,000-contract butterfly spread relies on the COB to match all three strike legs together rather than legging in separately and risking partial fills.
Risk & limitations
Complex order liquidity can be thinner than single-leg markets for unusual or wide strategies, occasionally resulting in wider effective net spreads than expected.
Examples are hypothetical, not trade recommendations. US contract and regulatory references do not automatically apply in Canada. Rules, margin requirements and broker policies can change; confirm them with the relevant authority and your broker.