Displayed liquidity is trading interest whose price and quantity are visible to market participants before execution, within the scope of a particular quotation or market-data feed. For a quant, it supplies an observable starting point for estimating trading capacity and execution cost. It does not reveal every possible counterparty or reserve that quantity for the observer's next order.
A displayed sell order offers shares to buyers; a displayed buy order offers to buy from sellers. In an order book, these quantities are organised by price. Displayed liquidity can refer to the size at the best quote, several price levels or the displayed book more broadly. A number without its side, price range, venue coverage and timestamp is incomplete.
“300 visible” does not mean “300 at the best price”
Consider an original synthetic stock snapshot from one venue at 14:30:00 UTC, on an illustrative trading day. We observe the following ask rows. Prices are USD per share and quantities are displayed whole shares.
| Ask price, USD/share | Displayed shares at this price | Cumulative displayed shares through this price |
|---|---|---|
| 101 | 100 | 100 |
| 102 | 200 | 300 |
There are 300 displayed shares across these two observed ask levels, but only 100 at the best ask of USD 101. The next 200 are offered at USD 102. Adding quantities across prices does not make those prices interchangeable.
Each row is an order-book level. Its size may aggregate multiple resting orders; the row alone does not establish their individual sizes or owners. The top of book would show only the first ask row on this side, alongside the best bid on the other side.
Original synthetic stock snapshot at 14:30:00 UTC on an illustrative trading day. Prices are USD per share; quantities are displayed whole shares. Both panels describe the same two observed ask levels, not confirmed executions or total market liquidity.
For an ask-price ceiling , cumulative displayed ask depth over the observed rows is
where is a displayed ask price and its displayed size. Here and shares. A ceiling between the two prices still includes only the first row. Below 101, neither observed row qualifies. This calculation describes the observed display; a ceiling above 102 cannot reveal levels absent from the feed.
A static execution model could consume these rows in price order if its matching assumptions allow that. The depth total itself establishes neither an average execution price nor a completed trade. The Order Books lesson develops that conditional calculation and its limits. It has a public preview; the full lesson requires membership.
Visibility has several boundaries
Feed coverage. A venue feed describes that venue. A consolidated product covers the venues and quotation types in its specification. A feed restricted to the best quote or a fixed number of levels leaves deeper interest unobserved. CME's MBO documentation illustrates the separate questions of price-level coverage and individual-order granularity: its market-by-price format aggregates quantities at a price, while market-by-order provides individual-order information. Extra granularity is not permission to infer every trader's total intended size.
Hidden interest. A lit market can display quotations while also accepting non-displayed interest. For example, Nasdaq Equity 4 describes non-displayed orders in Rule 4702(b)(3) and reserve replenishment in Rule 4703(h). An iceberg order exposes a displayed portion while withholding additional reserve. The visible sizes in our example provide no value for that reserve: neither zero nor a larger invented amount is established. Separate traders can also add new orders at the same price, so repeated display is not sufficient to identify an iceberg.
Time and access. A snapshot records an observation under its timestamp convention. Cancellations, competing executions and new orders can change the book before another order arrives. Whether the observer can access the quoted venue and meet its trading conditions also matters. The SEC's trade-execution explanation stresses that quotations cover specific quantities and prices may change before arrival.
In a backtest, retain the displayed snapshot as an input and model subsequent availability explicitly. Crediting a fill merely because enough shares appeared on screen confuses an observation with an outcome; adding arbitrary hidden shares makes the same error in the opposite direction.
Sources
- CME Group — Market by Order (MBO), “Background” and “MBP versus MBO”: aggregation, depth coverage and individual-order information.
- Nasdaq Equity 4, Rules 4702(b)(3) and 4703(h): non-displayed orders and replenishment from reserve. These are Nasdaq-specific examples, checked on 2026-10-27.
- SEC — Trade Execution: What Every Investor Should Know, last updated 16 January 2013: quoted quantity and changing prices before arrival. Used for the execution principle, rather than historical regulatory details.
- Narang, R. K. (2013), Inside the Black Box: A Simple Guide to Quantitative and High-Frequency Trading, 2nd ed., Wiley, Chapter 7, pp. 120–122 and 124–125: resting orders, depth and hidden interest. The numerical snapshot and figure are original.