Definition
An IOC order is an order type that attempts to execute immediately at the specified price or better, filling any portion that can be executed immediately and cancelling the unfilled remainder. IOC is used when a trader wants to take available liquidity without leaving a resting order on the book. IOC is distinct from FOK (fill or kill), which requires the entire quantity to fill immediately or the entire order to cancel.
Example
A trader submits an IOC buy order for 50 BTC at $95,000. If 35 BTC is available at $95,000 or lower, the order fills 35 BTC and cancels the remaining 15 BTC without leaving a resting order.
How Liquid Mercury Handles This
Mercury Pro supports the full institutional order-type vocabulary including IOC, FOK, GTC, GTD, iceberg, and peg orders across FIX, REST, and WebSocket surfaces with consistent semantics.