Arbitrage
Simultaneous purchase and sale of equivalent assets to profit from price discrepancies across markets.
Arbitrage is the practice of simultaneously buying and selling equivalent or identical financial instruments in different markets or forms to profit from a price discrepancy, with little or no net investment and theoretically no risk. Pure arbitrage exploits mispricing that violates the law of one price—the principle that the same asset should trade at the same price across markets after accounting for transaction costs and exchange rates. Classic examples include currency triangular arbitrage (exploiting inconsistent exchange rates across three currency pairs), covered interest rate arbitrage (profiting from interest rate differentials between countries using forward contracts to hedge currency risk), and index arbitrage (exploiting price differences between an index and its constituent stocks or futures). In practice, pure riskless arbitrage is rare and fleeting—high-frequency traders and sophisticated market participants with low transaction costs rapidly identify and close mispricing, restoring equilibrium. More commonly, practitioners engage in risk arbitrage (or statistical arbitrage), which involves positions where the expected profit is positive but outcomes are uncertain. Merger arbitrage, for example, buys the target company's stock after a deal announcement and shorts the acquirer, betting the deal closes at the announced price. Convertible bond arbitrage exploits pricing inefficiencies between convertible bonds and the underlying equity. Even so-called 'arbitrage' strategies carry significant risks—deals can fall through, correlations can break down, and in the short run markets can remain irrational longer than a fund can remain solvent, as the collapse of Long-Term Capital Management in 1998 illustrated. The existence of arbitrage activity is central to market efficiency theory: arbitrageurs serve as the mechanism that enforces the law of one price.
FAQs
Is true risk-free arbitrage possible in modern markets?
Pure risk-free arbitrage is extremely rare and short-lived in modern markets. High-frequency trading firms with low latency and transaction costs close most mispricings within milliseconds. Most strategies marketed as 'arbitrage' involve residual risk and are more accurately described as risk arbitrage or statistical arbitrage.
What is merger arbitrage?
Merger arbitrage involves buying shares of a takeover target after a deal is announced, at a slight discount to the announced acquisition price, and sometimes shorting the acquirer. The spread compensates for the risk that the deal fails. If the deal closes, the arb earns the spread; if it collapses, losses can be significant.
How does arbitrage contribute to market efficiency?
Arbitrageurs profit by identifying and trading on mispricings. As they do so, their buying and selling pressure moves prices toward equilibrium, eliminating the discrepancy. This continuous arbitrage activity is the market mechanism that enforces the law of one price and keeps related assets fairly valued relative to each other.
Related Terms
Alpha
Excess return of an investment relative to a benchmark index after adjusting for risk.
Efficient Frontier
Set of optimal portfolios offering highest expected return for each level of portfolio risk.
Modern Portfolio Theory
Framework for constructing investment portfolios to maximize return for a given level of risk.
FX Hedging
Using financial instruments to reduce currency risk exposure on foreign-denominated revenues or expenses.
