Arbitrage

What Is Arbitrage?

Arbitrage is a strategy that takes advantage of price differences for the same or very similar assets. An arbitrageur buys an asset where it is cheaper and sells it, or an equivalent asset, where it is more expensive, locking in a profit that is ideally free of market risk. Because the buying and selling happen at nearly the same moment, the trader does not need to predict which way prices will move.

How It Works

Arbitrage depends on the idea that identical assets should trade at the same price everywhere. When they do not, traders step in. Their buying pushes up the low price and their selling pushes down the high price, so the gap tends to close quickly. This is one reason arbitrage is often described as a force that helps keep markets efficient.

Common forms include:

• Spatial arbitrage, where the same stock trades at slightly different prices on two exchanges.
• Merger arbitrage, where a trader buys shares of a company being acquired and sometimes shorts the acquirer, betting that the deal closes at the announced price.
• Index arbitrage, where traders exploit gaps between a stock index futures contract and the value of the underlying stocks.

An Example

Suppose a share of a company trades for 100.00 dollars on one exchange and 100.50 dollars on another. A trader buys on the cheaper exchange and sells on the more expensive one at the same time, keeping the 0.50 dollar difference before costs. In practice, commissions, fees, taxes, and the time needed to execute both trades can eat up much or all of a small gap.

Risks and Limitations

Pure arbitrage is rare in large, liquid markets, because many well-funded traders compete to find and close these gaps. Real-world attempts also carry risks. Prices can move between the two trades, one side of a deal may fail to execute, and a deal expected to close may be delayed or cancelled. What looks like a risk-free profit on paper can become a loss in practice.

Why It Matters to Investors

Arbitrage helps explain why prices of related assets tend to move together and why large mispricings usually do not last long. For individual investors, understanding arbitrage can clarify how markets adjust and why apparent bargains are often quickly corrected.