The queue: FIFO and priority

When several limit orders wait at the same price, which one is filled first? On the CME Globex, for ES and NQ, the rule is FIFO (first in, first out): first come, first served. At the same price, the oldest order goes first. Your limit order therefore joins a queue, and your place in that queue decides whether you will be filled, and above all when.

This rule has a surprising consequence that every trader who works with limit orders must understand: getting filled easily is not always good news.