The mechanism is straightforward. When you place a market order, it matches against whatever orders are sitting on the other side of the order book at that moment. If you want to sell and the best bid (the highest price a buyer is currently offering) is lower than you expected, your market order still fills there. You get executed, but the price is whatever the book gives you. A limit order flips that trade-off. You name your price. If no one on the other side is willing to meet it, your order sits unfilled, sometimes for minutes, sometimes for days, sometimes never.
My position is that this is not a minor technical choice. A limit order trades certainty of execution for certainty of price. A market order does the opposite: it trades certainty of price for certainty of execution. Which one makes sense depends almost entirely on how liquid the stock is, meaning how many buyers and sellers are active in it and how tight the gap is between the best bid and the best offer.
In a heavily traded stock, this trade-off barely matters. Say a bank stock on the Nigerian Exchange has a bid of ₦28.00 and an offer of ₦28.05, with thousands of shares on each side and fresh orders arriving every few seconds. A market order to buy will fill at ₦28.05 or very close to it. The gap between what you expected and what you got, called slippage, is a few kobo. Using a limit order there buys you almost nothing, because the price was never going to move far from where you set it anyway.
Thinly traded stocks are a different animal. Picture a small-cap on the NGX with a bid of ₦5.20 and no offer at all, because the last seller pulled their order an hour ago and no one else has stepped in. If you place a market order to buy, there may be nothing to match against at a sensible price. Depending on how the exchange's system handles it, your order either sits waiting or fills against a stale, wide-spread quote far from ₦5.20. I am not describing any specific exchange's matching rules here, because they vary and this piece is not the place to state them. The general point holds regardless of mechanism: in a thin market, the price a market order actually achieves is less predictable, not more.
This is where the limit order earns its keep. If you set a limit to buy at ₦5.20, you will never pay more than that. You can wait a day for a seller to show up, or not get filled at all, but you know the worst case the moment you place the order. In a stock with low volume, sometimes just a few thousand shares changing hands in a session, that certainty is worth more than speed. The risk you are managing is not missing out on a quick move. It is paying a price that has no real support once you are the one who asked for it.
There is a cost on each side, and it is worth being honest about both. The cost of a market order is price risk: you might pay more or receive less than the last traded price, particularly in a stock where the gap between bid and offer is wide. The cost of a limit order is execution risk: your order might never trade, and the market might move away from your price entirely while you wait. Neither is a free option. The question an investor has to settle for themselves is which risk they can tolerate in the specific stock they are trading, not which order type sounds more sophisticated.
I have not covered here what fees or commissions a broker charges for each order type, because that varies by broker and platform, and nothing in a general discussion of mechanics can state a specific figure without being tied to one provider's fee schedule. Readers should check that directly with whoever executes their trades. Equally, I am not stating minimum tick sizes, order validity periods, or how any particular exchange prioritises orders in its queue, because those are exchange-specific rules, and this piece is deliberately staying on the general mechanics rather than any one market's rulebook.
The practical read is this: the thinner the stock, the more a limit order's price certainty is worth to you, and the more a market order's speed becomes a liability rather than a convenience. In a deep, liquid name, the two order types converge in outcome, so the choice matters less. The size of that gap between them, in any stock you are looking at, is really just a question of how many people are on the other side of the trade right now.
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