What it means
Picture an auction room that runs all day. Buyers post the highest price they will pay, sellers post the lowest price they will accept, and the system pairs them off whenever the two overlap.
That is the essence of an order-driven market, and it is how most major stock exchanges around the world operate. The order book is public in a basic sense.
It shows the best prices and how many shares are on offer at each level, so a trader can see the depth of the market before acting. Orders are generally matched on price first, and then by time, so the earlier order at a given price goes first.
The alternative is a quote-driven market, in which dealers (market makers) publish prices at which they will buy and sell and trade against their own inventory. Many real markets are hybrids, with an order book supported by designated market makers who step in when orders are scarce.
Understanding which type you are dealing with tells you who is providing liquidity and who sets the price. For a finance team, the key practical point is that large orders can move an order-driven market.
If you buy more than is available at the best price, your order "walks the book" and fills at progressively higher prices. That is why big buyers split orders and why thin, less popular shares can be expensive to trade.
In practice
Real-world examples.
Example
A retail investor places a limit order to buy 200 shares of a listed supermarket chain at $12.40 when the best offer is $12.45. The order sits in the book until a seller comes down to $12.40. The investor trades at the price they chose, but only if the market comes to them.
Example
A small exporter's treasurer uses an electronic platform to buy a futures contract that hedges commodity prices. The platform matches her bid against the best resting offer in the central book, and she can see prices and quantities before she commits. She pays no dealer margin on the price, only a small exchange fee.
Example
A founder selling shares in a freshly listed company watches the book thin out on the buy side one afternoon. He sees only 400 shares bid at the top price and decides to wait rather than sell his full block into a shallow market.
Formula
Calculation
Average fill price = total cost of all fills / total shares bought
Suppose the sell side of an order book shows 1,000 shares at $25.00, 1,500 shares at $25.02 and 2,000 shares at $25.05. A buyer places a market order for 3,000 shares. The fills are 1,000 x 25.00 = $25,000, then 1,500 x 25.02 = $37,530, then the remaining 500 x 25.05 = $12,525, giving a total of $75,055. The average fill price is 75,055 / 3,000 = about $25.018, which is $55 more than the $75,000 the buyer would have paid had all 3,000 shares been available at $25.00.Case study
Seen in the real world.
Cedarpoint Industries is a fictional manufacturer that listed on a regional exchange in this illustrative story. The CFO was surprised that when the company announced a share buyback, the price moved up more sharply than expected.
The investor relations team looked at the order book and found it was shallow: only a few thousand shares were offered within 2% of the market price. The company's broker, trading an order-driven market, was walking the book with every purchase.
The CFO asked the broker to release the buyback in small daily amounts rather than a single large purchase. The average cost came in lower, and the illustrative lesson was that in an order-driven market the shape of the book, not only the headline price, determines what you actually pay.
Watch out
Common mistakes.
- Assuming the last traded price is the price you can trade at, when in an order-driven market the available price depends on the orders currently in the book.
- Believing there is always a counterparty ready to trade, when thinly traded shares may have few orders on either side.
- Confusing order-driven with quote-driven markets, when in the latter a dealer commits capital to quote prices.
Questions
People also ask.
Is a stock exchange order-driven or quote-driven?
Most large modern exchanges are primarily order-driven, often with market makers added for liquidity support, so many are hybrids.
What does it mean when an order "walks the book"?
It means the order is large enough to use up the best-priced orders and then fill at progressively worse prices.
Why do order-driven markets show a bid-ask spread?
The spread is the gap between the highest buying price and the lowest selling price currently posted, and it narrows as more orders compete.
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