Payment for Order Flow and Best Execution

Payment for order flow (PFOF) is the practice whereby brokers receive payment from market makers for directing client orders. PFOF is a controversial topic, touching upon questions of conflict of interest, execution quality, and market fairness.

PFOF Mechanism

The essence of the practice: a retail broker (for example, Robinhood) receives a client order to purchase stocks. Instead of directing the order to an exchange, the broker passes it on to a wholesaler (a market maker such as Citadel Securities). The wholesaler executes the order from its own inventory and pays the broker for the “order flow.”

Economics for participants: the wholesaler earns from the spread (the difference between the execution price and the hedging price), paying a portion of the income to the broker. The broker monetizes the client flow, allowing them to offer “zero commission” trading. The client does not pay a commission, but do they receive the best price?

Internalization: the majority of retail orders are executed “internally” by the wholesaler, never reaching public exchanges. This reduces volumes on exchanges and potentially affects price discovery.

Arguments in Favor of PFOF

• Price improvement: wholesalers often execute orders at prices better than the NBBO (National Best Bid and Offer) on exchanges. A client placing a market order receives a price better than the best ask. Measurement of price improvement is a key argument for proponents.
• Zero commissions: PFOF enables brokers to offer commission-free trading, lowering barriers for retail investors. Democratization of investing allows more people to participate in the markets.
• Execution quality: wholesalers provide high fill rates (almost 100% execution), no information leakage (the order is not visible to the market), and fast execution. For small retail orders, this is arguably better than exchange competition.

Criticism of PFOF

• Conflict of interest: the broker has an incentive to send orders to whoever pays more, not to whoever executes better. Even if the broker chooses based on execution quality, the mere fact of receiving payment creates a potential bias.
• Hidden costs: “free” trading is not truly free—the client pays via the spread. But the spread is invisible to the client, unlike explicit commission. This can be misleading regarding the true costs.
• Market structure concerns: internalization decreases volumes on public exchanges, potentially degrading price discovery. If a significant portion of trades occurs off-exchange, exchange prices may not reflect true supply and demand.
• Two-tiered market: retail orders are directed to wholesalers, institutional orders go to exchanges. This creates a segmented structure with different treatment for different investors.

Best Execution Obligation

Best execution is a regulatory requirement to execute client orders under the best available conditions. The definition of “best” is multifactorial: price, speed, likelihood of execution, size, nature of the order.

SEC Rule 606: requires disclosure from brokers about routing practices and PFOF payments. Clients may request details about execution of specific orders. Transparency as a regulatory tool.

SEC Rule 605: requires market centers to publish execution quality statistics. Allows comparison of venues by price improvement, speed, fill rates.

Regulatory Discussions

SEC review: SEC Chair Gary Gensler initiated a review of the equity market structure, including PFOF. Discussed options include a complete ban on PFOF (as in the United Kingdom, Canada), an auction mechanism for retail orders, and enhanced disclosure.

European approach: MiFID II effectively banned PFOF in most European jurisdictions. The argument: payments create an inherent conflict incompatible with best execution.

Proposed reforms: order-by-order competition (each order is submitted to an auction), minimum price improvement requirements, consolidated tape for all executions. The discussion continues.

Practical Aspects for Investors

• Understanding routing: investors should understand where their orders are sent. Many brokers allow choosing routing—direct market access versus wholesaler.
• Order types matter: limit orders give clients more control over the price than market orders. With a market order, you rely on the venue’s execution quality.
• Broker selection: when choosing a broker, in addition to commissions, you should consider execution quality reports (Rule 606, 605), transparency about practices, and available routing options.
• Size matters: for small retail orders, the PFOF system may be acceptable. For larger orders or sophisticated strategies, direct market access may be preferable.