What Is a Market Order? Definition & Example

A market order executes right now against whatever prices are resting in the order book. You are guaranteed to fill; you are not guaranteed a price. In a liquid market that distinction is trivial. In a thin or fast-moving one it can be expensive.

The mechanics matter for larger orders. A market buy consumes the cheapest sell offers first, then the next cheapest, walking up the book until the full size is filled. If your order is large relative to available depth, the later portions fill at meaningfully worse prices than the first — this is slippage, and it scales with your size relative to the book.

Market orders always pay the taker fee, because they remove liquidity rather than provide it. On Hyperliquid that is 0.035% per side, so a round trip costs 0.07% of notional. That is negligible once and substantial two hundred times.

Use a market order when execution certainty is worth more than price: exiting a position that has gone wrong, entering a fast-moving breakout you cannot afford to miss, or closing anything during a volatility event. In a genuine crash, the market order that fills you 2% worse than you hoped is the one that got you out at all.

Before sending a large market order, glance at the order book depth. If your size is a significant fraction of what is resting within a few ticks, split it or use limits — the slippage on a single oversized market order in a thin book routinely exceeds the entire fee saving people optimise for elsewhere.