Market Making Explained: How Elite Firms Actually Make Money
Market making is the strategy behind Jane Street, Optiver, and Citadel Securities. Here's how it actually works.
Market makers quote two prices:
- Bid: The price they'll buy at (lower)
- Ask: The price they'll sell at (higher)
Let's say Apple stock trades around $150. A market maker might quote:
- Bid: $149.99
- Ask: $150.01
When someone wants to buy Apple stock immediately, they hit the ask ($150.01). When someone wants to sell immediately, they hit the bid ($149.99).
The market maker makes $0.02 per share on every completed round-trip trade.
Why This Actually Works
You're probably thinking: "Two cents per share? That's nothing."
Scale changes everything. Jane Street trades millions of shares per day across thousands of different stocks. Those pennies add up fast.
But here's the catch: it's not risk-free money. Market makers face two big problems.
Problem 1: Adverse Selection
Some traders know things you don't. When they buy from you at $150.01, they might know the stock is about to jump to $155. You just sold at $150.01, and now you're holding inventory that's dropping in value.
Market makers are wrong about direction more than half the time. They make money by being wrong slightly less than the spread compensates for.
Problem 2: Inventory Risk
After 1,000 trades, you might own 50,000 shares of Apple and be short 30,000 shares of Microsoft. That's a lot of market exposure. If both stocks move against you overnight, you lose real money.
How the Professionals Do It
Firms like Jane Street and Optiver have solved these problems with technology and math:
Speed: Their algorithms update quotes hundreds of times per second. When new information arrives, they're often first to adjust prices.
Diversification: They make markets in thousands of instruments. A loss in Apple might be offset by gains in Treasury bonds.
Hedging: They don't just hold naked inventory. They use derivatives and related instruments to offset directional risk.
Statistical models: They've built sophisticated models to predict when adverse selection is likely and adjust spreads accordingly.
Interview Questions You'll Actually See
If you're interviewing at market-making firms, expect questions like:
"Make a market in the sum of three dice" This tests whether you can quickly calculate expected value and think about both sides of a bet.
"I'll flip a coin with unknown bias. Make a market in whether it lands heads" This tests how you handle uncertainty and adverse selection.
"You've bought 1,000 shares and the stock has moved against you. What's your new bid/ask?" This tests whether you understand how inventory affects pricing.
These aren't testing your market knowledge. They're testing whether you can think probabilistically under pressure.
Why Market Making Matters for Markets
Before electronic market making, bid-ask spreads were much wider. It cost regular investors a lot more to buy and sell stocks.
HFT market makers have compressed spreads dramatically. What used to cost 12.5 cents per share in the 1990s now costs 1-2 cents. That's saved regular investors billions of dollars.
The trade-off? Markets are much faster and more complex now. The old human specialists who used to make markets can't compete with algorithms that react in microseconds.
The Skills That Actually Matter
Successful market makers are good at:
Mental math: You need to calculate expected values quickly and accurately.
Staying calm under pressure: When you're losing money fast, you can't panic and make bad decisions.
Adapting quickly: Market conditions change constantly. What worked yesterday might not work today.
Understanding probability: Every market making decision is essentially a probability calculation.
Is It Hard to Break In?
The technical bar is high. Firms like Optiver and Jane Street interview almost exclusively math, physics, and computer science majors. You need to be comfortable with probability, statistics, and programming.
But they don't expect finance knowledge. I know people who got offers without ever owning a stock. They care about raw analytical ability, not whether you've read the Wall Street Journal.
The Bottom Line
Market making is how some of the smartest people in finance make money. It's not about predicting the future or finding the next hot stock. It's about being faster and smarter than other market participants, thousands of times per day.
If you can handle the pressure and have the math skills, it pays extremely well. If you can't, the markets will humble you pretty quickly.