Market makers and liquidity providers: who stands between the buyer and the seller

An investor who buys 100 shares at USD 50.05 is not, in most cases, buying directly from another investor who is selling at USD 50.05 at exactly the same moment. They are buying from a market maker—a firm whose business is to continuously quote both bids and asks on the security and to facilitate trades by holding inventory between the moments when natural buyers and sellers arrive. Market makers and other liquidity providers are the structural intermediaries that make continuous trading possible.

What market makers are

A market maker is a firm or trading desk that commits to continuously providing both buy and sell quotes for a defined set of securities. The market maker earns the spread between the bid and the ask when both sides are hit over time; in exchange, the firm bears the risk of holding inventory positions in either direction whenever one side of the spread is hit more frequently than the other.

Market making was originally a designated role at the major exchanges. The NYSE specialist (renamed to Designated Market Maker after 2008) was the assigned market maker for each listed stock, with specific obligations to maintain orderly trading. The NASDAQ market structure has always allowed multiple competing market makers per stock; modern equity markets have evolved into competitive structures where many firms quote on each security, with the tightest quotes winning the immediate order flow.

The dominant modern market makers are high-frequency trading firms (Citadel Securities, Virtu, Jane Street, Optiver) that combine sophisticated inventory management with very fast execution to provide continuous liquidity at tight spreads. The economic role they play is the same as the historical market maker; the technical implementation is much faster and operates across many more securities and venues simultaneously.

How they work

The market maker's basic operation is symmetric. The firm posts a bid (say, USD 49.95) and an ask (say, USD 50.05). When an incoming buy order hits the ask, the market maker sells from inventory or shorts the stock; when a sell order hits the bid, the firm buys into inventory or covers a short. Over many trades, the firm earns the average of (ask − mid) on sells and (mid − bid) on buys, which sums to the spread it captures per round-trip.

The risk is one-sided fill imbalance. If buyers consistently outnumber sellers for a period (because of news, sentiment, or other factors), the market maker's inventory builds in a short position; the firm must either find a way to cover the short (lift the offer in another venue, accept worse pricing, hedge with derivatives) or widen its quotes to discourage further one-sided flow. Symmetric situations build long inventory; the firm must work down the position over time.

Modern market makers manage inventory across many securities simultaneously. A long inventory in one stock can be hedged with a correlated short in another; a long stock can be hedged with a short ETF; a long single name can be partially offset with a short index future. The cross-asset hedging makes individual-name market making more capital-efficient than it would be in a single-asset framework.

The compensation for the activity is the bid-ask spread captured plus, in many venues, exchange-paid liquidity rebates that pay a small fee per share to liquidity providers. The rebate is the exchange's incentive to attract liquidity; it allows market makers to quote tighter spreads than the spread alone would justify. Critics argue the rebate distorts the market microstructure; defenders argue it produces better execution for end investors.

What the evidence shows

The shift to electronic, competitive market making has dramatically tightened spreads and increased depth. Average effective spreads on US large-cap stocks in 2025 are 80–90% tighter than they were in 2000, and the depth at the inside quotes is materially deeper. The improvement is largely attributable to high-frequency liquidity providers replacing older specialist and dealer market-making models.

The competitive dynamics have also created some structural concerns. The concentration of liquidity provision in a small number of high-frequency firms means that a single firm's withdrawal can produce material spread widening; the May 2010 flash crash was partially attributable to liquidity providers stepping back at the same moment, leaving the order book briefly unsupported. Regulatory frameworks (Limit-Up Limit-Down, the Market Access Rule) have been introduced to address these dynamics, with mixed evidence on their effectiveness.

For end investors, the empirical case is broadly positive. The cost of executing a typical trade is materially lower than it was a generation ago, and the depth available at the inside quotes is sufficient for most retail orders to execute without market impact. The market-microstructure debate is real but has not been a meaningful drag on retail-investor outcomes.

Limitations and trade-offs

Market makers' commitment to continuous quoting is conditional on the conditions remaining within their risk-management parameters. In genuinely extreme market regimes—flash crashes, sustained one-directional pressure, news-driven dislocations—market makers can and do widen quotes, withdraw liquidity, or stop quoting entirely. The depth that exists in normal markets is not guaranteed in stress.

The interaction between market makers and the broader market structure is complex. Payment-for-order-flow arrangements (where retail brokers route customer orders to specific market makers in exchange for payment) are economically efficient for the brokers and the market makers but raise questions about whether retail investors get the best available execution. The regulatory framework around these arrangements has been contested.

For long-term retail investors trading infrequently in liquid securities, the market-maker dynamics are largely invisible. The spread paid is small; the execution is reliable; the broader microstructure operates without the investor needing to understand its specifics. The dynamics matter most for active traders and for trading in less-liquid securities where market-maker depth is more variable.

Market makers in pfolio

Market makers and other liquidity providers are exchange-side participants that facilitate trade execution. pfolio's analytics work from the resulting trade prices regardless of the market structure that produced them. Bid-ask spreads, which compensate market makers for providing liquidity, are reflected in the actual trades but not separately tracked by the platform.

Related articles

• Bid-ask spreads: the cost of trade execution embedded in every transaction
• ETF liquidity explained: bid-ask spreads, premium, and discount to NAV
• Stock exchanges and trading venues: NYSE, NASDAQ, LSE, and how exchanges differ
• Transaction costs in systematic investing: spread, slippage, and market impact