Market Makers: Definition, Compensation, and the Mechanics of the Bid-Ask Spread

Market makers are firms or individuals that profit by simultaneously offering to buy and sell a security or contract, standing ready to execute both sides of a transaction. They earn revenue through the bid-ask spread: the difference between the price at which they buy and the price at which they sell. This paper explains the economic function of market makers, the mechanisms by which spreads compensate them, and the core risks that justify their existence as a distinct role in financial markets.

What a Market Maker Is

A market maker commits capital and infrastructure to maintain liquidity in an asset. Unlike a dealer who may occasionally buy and sell, or a broker who matches buyers and sellers without risk, a market maker holds inventory of assets temporarily: it purchases from sellers and resells to buyers, or sells short and covers by buying back. The defining feature is continuous two-sided quoting, often enforced by exchange rules ^[1]. In equity markets, market makers may be required to display buy and sell quotes at all times during trading hours. In derivative markets like futures and options, market makers post bids and offers in order books on exchanges like the CME Group and Cboe ^[2].

Market makers exist across all major financial markets: equities, bonds, foreign exchange, derivatives, and cryptocurrencies. They vary in size from large proprietary trading firms managing billions in daily volume to individual futures traders quoting single contracts. Some operate under official designations like Nasdaq Market Makers or NYSE Specialists (now Designated Market Makers ^[1]); others operate as plain participants in electronic order books with no special obligation.

What Market Makers Are Paid For

The market maker's income comes from the spread. A simplified example: a market maker quotes a buy price (bid) of $99.95 and a sell price (ask) of $100.05 for a stock trading at approximately $100. If a buyer market-orders at $100.05, the maker buys at that price and owns the stock. If a seller then market-orders at $99.95, the maker sells the stock at that price, capturing a $0.10 profit (the spread) on a $100 position. Scale this across thousands of transactions daily, and the spread is the business model.

The spread compensates the market maker for three distinct economic functions ^[3]. First, it covers the operational cost of maintaining infrastructure: computer systems, exchange fees and membership, staff, and office overhead. These costs are real and substantial for professional market makers. Second, the spread compensates the maker for the risk that the position moves against it before it can lay off the acquired inventory. This is called inventory risk: if a market maker buys a stock at $99.95 and the price falls to $99.00 before it can sell, it loses money ^[3]. Third, and most controversial in academic theory, the spread compensates for adverse selection risk: the cost of trading against counterparties who possess superior information ^[3].

Why Spreads Exist: The Economic Function

Spreads are positive (bid < ask) because of the combination of these costs. Without spreads, market makers would be indifferent between buying at a fair price and selling at that same price, earning nothing for their service. The market would have no mechanism to create liquidity.

Inventory risk is straightforward: a market maker that buys has exposure to price moves. A trader who buys a single share of a stock that then declines $1 incurs a real loss. A market maker that buys thousands of shares and the stock declines proportionally incurs a larger loss. To cover the expected loss from adverse price moves, the market maker must earn a premium on successful trades. This premium is the spread. The wider the potential price swings (volatility), the wider the spread must be to compensate for inventory risk ^[3].

Adverse selection risk, formalized in the microstructure literature, reflects the possibility that a counterparty who wants to trade may know something the market maker does not. If a stock's fundamental value is truly $100 but the market maker quotes bids and asks, and an informed trader arrives with private knowledge that the stock will rise to $110, the informed trader will buy at the maker's ask price. Over time, market makers will lose money selling to informed traders and buying from uninformed traders. To protect against this, market makers widen spreads. The wider the spread, the less attractive it becomes for informed traders to take one side, and the more insulated the market maker is from informed trading losses ^[3].

Operational costs are also real. An individual futures trader quoting single contracts incurs exchange fees per transaction. A large equity market maker operates data centers, employs risk managers, and pays regulatory compliance staff. These costs must be covered by the spread.

Mechanical Example

Consider a simplified scenario in Treasury futures. The CME Group 10-year Treasury note futures contract trades with a quoted spread of 0.5 basis points (0.005 points) in normal market conditions ^[2]. One contract controls $100,000 of face value. A spread of 0.005 points translates to approximately $50 per contract round-trip (buy and sell one contract). A market maker that executes 500 contracts per day, half of which involve inventory (buying and then selling the same contract), nets approximately $12,500 per day in gross spread income at 0.5 basis points, ignoring slippage and adverse fills. If the market maker operates 250 trading days per year, that is $3.125 million in annual gross spread income from routine market-making activity. From this, the firm must pay exchange fees, infrastructure costs, salaries, and absorb losses from inventory moves. During volatile periods in 2020, spreads on Treasury futures widened to 1-2 basis points or more, reflecting higher inventory and adverse selection risk ^[2].

Limitations and Critical Observations

Several significant limitations constrain this model.

First, the empirical relationship between volatility, adverse selection, and spreads is well-established in academic microstructure research, but the relative contribution of each factor varies by market and is difficult to measure in practice. Claims that "spreads exist primarily because of adverse selection" or "primarily because of inventory risk" cannot be definitively proven with observational data alone, because these factors are correlated with market conditions ^[3].

Second, not all financial markets have traditional market makers. Many electronic markets operate via pure order books with no designated makers, and spreads emerge from the actions of numerous limit-order providers with no special role ^[2]. In these markets, the economic logic is similar, a limit order provider assumes inventory and adverse selection risk, but the compensation structure is less transparent.

Third, regulatory changes and technology shifts have eroded the profitability of traditional spread-based market making. The rise of algorithmic trading and high-frequency trading has compressed spreads dramatically over the past two decades, particularly in liquid equities. Some academic research suggests that spreads in highly liquid assets now reflect primarily operational costs, with adverse selection and inventory risk playing a smaller role ^[3]. This raises the question of whether the model applies universally or only to less liquid, more volatile assets.

Fourth, the "adverse selection" argument assumes information asymmetry between the market maker and the public. In modern markets with real-time dissemination of information and regulatory restrictions on insider trading, the degree of information asymmetry is limited. Spreads may widen during earnings announcements not because of information risk, but because inventory risk (volatility) increases sharply.

Fifth, the described model assumes the market maker is a rational profit maximizer. In practice, regulation, exchange requirements, and market fragmentation may force market makers to quote spreads wider than economic fundamentals would justify. A market maker obligated to maintain bids and offers under exchange rules may be forced to absorb losses during extreme dislocations.

Lastly, this framework is most applicable to large, liquid, standardized instruments (equities, index futures, major currency pairs, Treasury bonds). For illiquid assets or long-dated derivatives, spreads reflect the three factors above and the maker's difficulty in hedging or laying off the position. A market maker in a thinly traded commodity has to maintain an inventory buffer for much longer and at greater cost.

Summary

Market makers provide a specific service: the absorption of immediate execution risk. They simultaneously stand ready to buy and sell, assuming the temporary inventory and the risk that they must find a counterparty on the other side at an adverse price. The bid-ask spread is their compensation for this service. The spread covers three costs: operational expenses, losses from adverse price movement (inventory risk), and losses to informed traders who exploit information asymmetries (adverse selection risk). The width of the spread reflects market conditions, the stability of the asset, and the quality of market-making infrastructure available. Understanding spreads not as arbitrary profit margins but as the price of liquidity is essential for traders who execute in real time and for investors evaluating transaction costs.

Key Definitions

Bid-ask spread: The difference between the highest price a market maker will pay to buy a security (bid) and the lowest price at which it will sell (ask); the market maker's primary source of revenue.

Adverse selection: The risk that a counterparty to a trade possesses information superior to the market maker's, causing the maker to systematically sell to informed buyers and buy from informed sellers.

Inventory risk: The risk that a market maker's temporary holding of a position declines in value before it can be offset by a trade with a counterparty.

Market maker: A firm or individual that provides liquidity by maintaining simultaneous bid and ask prices for a security or contract, absorbing the risk of holding the position temporarily.

Liquidity: The ability to buy or sell an asset quickly without substantially moving the price; more liquid assets typically have narrower spreads.

Order book: A display of all outstanding buy and sell orders for a security, organized by price level.

Designated Market Maker (DMM): An individual or firm assigned by an exchange to maintain liquidity in specific securities, typically subject to quoting obligations; formerly called a specialist on the NYSE ^[1].

References

1. U.S. Securities and Exchange Commission, "Market Makers," SEC.gov (year not specified). Https://www.sec.gov/files/Market_Makers.pdf (primary source: SEC regulatory guidance)

2. CME Group, "10-Year U.S. Treasury Note Futures Contract Specifications," CME Education. Https://www.cmegroup.com/education (primary source: exchange contract specifications)

3. Maureen O'Hara, "Market Microstructure Theory," Blackwell Publishers, 1995; and academic research on bid-ask spreads and market making available via doi.org and SSRN. (Secondary interpretation; the specific empirical studies on adverse selection and inventory models are documented in peer-reviewed journals referenced by O'Hara's full treatment.)

Educational research on historical data only. Not investment advice, not a signal, and never a performance promise. Past results do not predict future performance. Every reference is link-verified before publication and every paper is re-audited weekly against the library's editorial standard.

Last reviewed by the PropLedger research pipeline: 2026-10-19. Educational research on historical data, not financial advice.