Agency execution means arranging or executing a trade for a client’s account as the client’s agent. The client acquires or sells the investment; the intermediary provides execution services, commonly for a commission or fee. For a quant comparing brokers, this separates the amount invested from the cost of getting the trade done.
A broker can route an order to a trading venue, work it through an execution algorithm, or arrange a trade with another participant. “Agency” describes the capacity in which the firm acts. It does not specify a particular venue, order type or degree of automation.
A purchase amount is not broker revenue
Suppose a fictional broker acts solely as agent for a client buying 100 shares at USD 100 per share, and charges a separate USD 10 agency fee. The order fills in full. Ignore taxes, other charges and funding, and leave settlement timing unspecified.
The client’s cash outlay is
Of that total, USD 10,000 is security consideration: the amount paid for the shares. The broker’s stipulated fee income is USD 10 before expenses. Processing the client’s purchase does not make the security consideration the agency broker’s revenue. The client ends up holding the 100 shares and bears their subsequent investment gains and losses.
Original synthetic agency purchase in USD. The diagram shows economic allocation, not the route taken by settlement cash or securities. Only the stated agency fee is included; settlement timing is unspecified.
The fee is also only one part of the client’s transaction cost. Spread, price movement while an order is worked and the order’s own market impact can affect the result. A lower commission therefore does not, by itself, establish a better execution service.
Capacity and execution quality are different questions
In principal trading, the intermediary buys or sells for its own account. A dealer selling shares from its own book to a customer is acting as principal on that trade. In the agency example, the broker executes the client’s purchase rather than selling its own investment to the client. The same firm can operate in different capacities on different transactions; a familiar firm name or the presence of a fee does not establish capacity.
Agency does not promise a fill, a particular execution price or freedom from conflicts. Nor does principal capacity automatically remove best-execution duties. For U.S. FINRA members, Rule 5310(a) and (e) requires reasonable diligence to find the best market under prevailing conditions and expressly applies to both agency and principal customer transactions. The terms of the order, transaction size, market conditions and accessible quotes matter. This is a duty concerning execution under the circumstances, rather than a guarantee of the best price later visible in hindsight.
Customer instructions also matter. Rule 5310’s Supplementary Material .08 limits the determination beyond an unsolicited customer instruction to use a particular market, while retaining prompt processing in accordance with the order. Its .09 execution-quality review considers price, execution likelihood, speed, size and costs, among other factors. These U.S. requirements should not be assumed to describe every jurisdiction or instrument.
For ordinary U.S. customer stock trades, the confirmation is an important capacity record. SEC Rule 10b-10(a)(2) requires disclosure of agency or principal capacity and sets remuneration disclosures; FINRA Rule 2232(a) requires member confirmations to conform to that rule. Read the capacity and charges together, rather than inferring the relationship from a cash debit alone.
The Market Participants lesson places brokers and dealers within the wider execution, clearing, settlement and custody chain (public preview; full lesson requires membership). That distinction also helps explain why acting as agent does not mean the intermediary has no operational or settlement responsibilities.
Sources
- SEC: Guide to Broker-Dealer Registration, II.A–B — agency and own-account roles. This older guide is used for the capacity distinction.
- FINRA Rule 5310: Best Execution and Interpositioning — U.S. member duties in agency and principal transactions, customer instructions and execution-quality review.
- SEC Rule 10b-10, 2025 CFR edition, (a)(2) and FINRA Rule 2232(a) — capacity and remuneration disclosures for covered U.S. customer trades.
- Rishi K. Narang, Inside the Black Box: A Simple Guide to Quantitative and High-Frequency Trading, 2nd edition, Wiley, 2013, Chapter 5, pp. 80–81, and Chapter 7, pp. 117–118 — commissions versus other execution costs, broker infrastructure and algorithmic execution. The numerical example and figure are original.