Arbitrageur

An arbitrageur is a trader, fund or firm that seeks to profit from price differences for the same asset, or closely related assets, in different markets or forms. The classic arbitrageur buys where the asset is cheaper and sells where it is more expensive at the same time, locking in the gap. In practice most arbitrage involves some risk, and arbitrageurs range from banks and hedge funds to automated trading firms and individual crypto traders.

Arbitrageurs carry out arbitrage, the activity, and their trading plays an important role in price discovery: by exploiting gaps, they push prices back into line. The efficient market hypothesis and the arbitrage pricing theory both rely on arbitrageurs to keep markets consistent. Arbitrageurs are often contrasted with speculators, who take outright bets on price direction.

Imagine apples sell for $1 in one town and $1.30 in the next. Someone who buys a cart of apples in the first town and sells them in the second earns the difference, minus the cost of the trip. That person is an arbitrageur. If enough people do the same, apples get dearer in the first town and cheaper in the second until the gap is just the cost of transport.

Financial arbitrageurs do this with shares, currencies, bonds and crypto, often in fractions of a second. The gaps they chase are usually tiny, so they rely on speed, low costs and large volumes.

• Spatial or cross-market. Buying an asset on one exchange and selling it on another, such as the same share listed in two countries.
• Currency. Exploiting inconsistent exchange rates, including triangular arbitrage across three currencies, described under currency arbitrage.
• Merger or risk arbitrage. Buying shares of a takeover target below the offer price and betting the deal will close.
• Convertible and capital structure. Trading mispricings between a company's bonds, convertibles and shares.
• Statistical. Using models to trade baskets of securities whose prices usually move together, often with high-frequency trading systems.
• Basis and funding. Trading the gap between spot and futures prices, or capturing a funding rate on perpetual futures.

Crypto markets are fragmented across hundreds of exchanges, which creates frequent price gaps. Arbitrageurs move coins between venues when prices diverge, sometimes earning large spreads in markets with capital controls, as with the kimchi premium in South Korea. On blockchains, bots trade between automated market makers whenever a pool's price drifts from the wider market, and some use flash loan arbitrage to borrow and repay capital within a single transaction. Basis traders buy spot bitcoin and sell futures to capture a premium. Competition among on-chain arbitrage bots for profitable transactions is closely linked to maximal extractable value and to front-running concerns.

Arbitrageurs make markets more efficient by linking prices across venues and instruments. Their trading narrows spreads, adds liquidity and helps exchange-traded funds track their underlying assets, since arbitrageurs create and redeem fund shares when prices diverge. They also tie futures prices to spot prices and keep currency cross rates consistent. In decentralized finance, arbitrage is how AMM pool prices follow the market, though arbitrage profits come partly at the expense of liquidity providers.

Real arbitrage is rarely risk-free:

• Execution risk. Prices can move before both legs of a trade are completed.
• Transfer and settlement risk. Moving assets between exchanges takes time, and withdrawals can be delayed or frozen.
• Counterparty risk. An exchange or broker may fail while holding the arbitrageur's funds.
• Funding and leverage. Small spreads often require borrowed money, so losses can grow quickly.
• Deal risk. In merger arbitrage, a blocked deal can wipe out months of gains.

The economists Andrei Shleifer and Robert Vishny argued in a 1997 paper that these limits mean mispricings can persist and even widen, forcing arbitrageurs to sell at the worst time. The 1998 collapse of the hedge fund Long-Term Capital Management, whose relative-value trades went wrong as spreads widened, is the classic example.