What Is the Difference between Price-Time Priority and Pro-Rata Order Matching?

Price-time priority is a standard order matching rule where the best price is matched first, and among orders at the same price, the one submitted earliest in time is matched first. Pro-rata matching, conversely, also prioritizes price, but for orders at the same best price, the remaining volume is distributed proportionally based on the size of each order.

Price-time is common for single-venue CEXs, while pro-rata is often used in futures or options markets.