What Is Arbitrage?
Arbitrage is the practice of profiting from price differences of the same or equivalent asset across different markets, with little or no net risk.
What Is Arbitrage?
Arbitrage is the simultaneous purchase and sale of the same (or equivalent) asset in different markets to profit from a price discrepancy. In a textbook arbitrage, the buy and sell legs execute near-simultaneously, leaving the trader with a locked-in profit and minimal market risk.
The basic idea
If an asset trades at $100 on Exchange A and $101 on Exchange B, you can:
- Buy at $100 on Exchange A.
- Sell at $101 on Exchange B.
- Pocket the $1 difference (minus fees).
The trade is "risk-free" only if both legs fill at the expected prices — which is why real arbitrage is harder than it sounds.
Common types
| Type | Description | Example |
|---|---|---|
| Spatial | Same asset, different venues | Stock on two exchanges |
| Triangular (forex) | Cross-rate mismatch | EUR/USD × USD/JPY vs EUR/JPY |
| Statistical | Cointegrated pair reverts to mean | Long Coke, short Pepsi |
| Merger / event | Acquirer vs target pricing | Buyout at fixed ratio |
| Cash-and-carry | Spot vs futures gap | Buy spot, sell futures, hold to expiry |
| ETF vs basket | ETF price vs underlying NAV | ETF trades at premium to basket |
Worked example: cash-and-carry
A stock trades at $100 spot. The 1-year futures contract prices it at $104. Risk-free rate is 4%.
- Fair futures price = $100 × (1 + 4%) = $104.
- If futures trade at $106 → arbitrage opportunity:
- Borrow $100 at 4%.
- Buy the stock at $100 spot.
- Sell the futures at $106.
- At expiry, deliver the stock for $106, repay $104 loan → $2 risk-free profit.
Why arbitrage is rare for retail
- Speed. Professionals with co-located servers compete in microseconds. By the time you see the gap, it's usually gone.
- Fees. Spreads, commissions, and funding costs often exceed the price gap.
- Capital. Profitable arbitrage typically requires large notional to clear meaningful dollars after costs.
- Settlement risk. Different venues settle at different times; things can move in between.
- Borrowing costs. Many arbitrages require shorting or borrowing — both expensive.
Arbitrage's role in the market
Arbitrageurs are the market's price-keepers. Their activity keeps ETF prices close to NAV, aligns futures prices with spot, eliminates obvious cross-market pricing gaps, and provides liquidity. Without arbitrage, the same stock could trade at meaningfully different prices on different venues — and the cost of trading would be higher for everyone.
Bottom line
Pure arbitrage is a real but rare phenomenon that professionals hunt in microseconds. For beginners, the value of understanding arbitrage is conceptual: it explains why prices stay aligned across markets, why ETFs track their baskets, and why "obvious free money" is almost never free. If you spot an arb that looks too good, check the fees, the settlement, and the borrow costs before celebrating.