Arbitrage is the practice of buying and selling the same or closely equivalent asset at the same time in different markets to capture a price gap. The goal is to lock in a small, low-risk profit that exists because prices are out of line for a brief moment.
In textbook form, you buy where it is cheaper and sell where it is dearer, then pocket the difference after fees and funding costs. In the real world, it relies on speed, reliable execution and a clear view of all costs.
Why do price gaps appear at all
Markets do not update in perfect sync. Quotes change every millisecond, trading venues are fragmented, and information travels with tiny delays. That is enough to create short-lived mismatches. Other causes include:
- Different buyer and seller flows. One exchange might have a wave of buyers while another is quiet, nudging the price higher only in one place.
- Trading hours and settlement rules. If one market is open and the other is shut, news can move the open venue first. Settlement timing and short-selling rules vary, which can hinder quick alignment.
- Funding and borrowing costs. Futures, options and margin financing embed interest rates and dividends. These carry costs create a theoretical fair value that can deviate from the spot price.
- Operational frictions. Transfer delays, blockchain congestion in crypto, and custody limitations can stop capital from moving instantly.
These gaps usually close fast as arbitrageurs act. That activity is one reason related prices tend to track each other so closely during normal conditions.
A simple worked example
Imagine the same company trades on two venues at the same time. Venue A shows 100.00 to buy and 100.10 to sell. Venue B shows 100.40 to buy and 100.50 to sell. You can buy at 100.10 on A and sell at 100.40 on B. The headline spread is 30 pence per share.
Assume you execute 2,000 shares instantly, paying 0.05 per share in total fees and taxes across both venues. Your gross difference is 0.30 per share. Net profit is 0.30 minus 0.05, so 0.25 per share, or £500 on 2,000 shares. If you need to borrow stock to sell first, borrowing fees reduce this further. If you face currency conversion, that cost also bites.
If either order slips by a tick, or only part fills, your margin can vanish. That is why arbitrage is often automated and size is kept in line with available liquidity.
Common forms of arbitrage you will come across
- Exchange to exchange. The most straightforward case. Buy an asset on one exchange and sell it on another where the price is higher. In crypto, this is often called spatial arbitrage, but transfer times and withdrawal limits matter.
- Cross-listing and receipts. Shares listed in multiple countries, or represented by an ADR, should track each other after adjusting for exchange rates and ratios. When they do not, traders use swaps or conversions to realign prices.
- ETF versus basket. An exchange traded fund should trade close to the value of its underlying basket. If the ETF is rich, authorised participants can sell the ETF, buy the basket, then create new ETF units. The reverse applies if the ETF is cheap. The creation and redemption process is what keeps the price in line.
- Cash and carry. Buy the spot asset and sell a futures contract when the future trades above fair value. Hold the spot, deliver into the future at expiry, and earn the locked-in spread minus funding, storage and fees. In crypto, a similar idea appears when perpetual swaps have rich funding rates.
- Triangular FX arbitrage. Use three currency pairs to exploit a mispriced cross rate, for example converting GBP to USD, USD to EUR, and EUR back to GBP when the implied rate is off. All three legs must be near-simultaneous.
- Merger or risk arbitrage. Often called arbitrage in the market, though it carries event risk. Buy the target and sometimes short the acquirer after a deal is announced, aiming to capture the spread to the offer price if the deal closes.
What can go wrong
Arbitrage sounds neat on paper. In practice, the following frictions and risks can erase or reverse the profit:
- Execution and leg risk. One side fills and the other does not, leaving you with an unwanted position. Fast markets make this more likely.
- Slippage and fees. The visible spread may disappear by the time your order hits. Commissions, exchange fees, stamp duties and network fees in crypto can exceed the gap.
- Transfer and settlement delays. Moving cash, securities or tokens takes time. Blockchain congestion or bank cut-off times can strand capital while the spread closes.
- Borrow and locate constraints. Shorting may be restricted or expensive. If you cannot borrow the asset, you might be forced to buy it back at a loss.
- Corporate actions and dividends. Entitlements differ by settlement date and line of stock. A dividend or rights issue can change the economics during your hold.
- Model error. In futures and options, a wrong assumption about interest rates, dividends, funding or storage can turn an apparent bargain into a fair price.
- Platform or venue risk. Outages, trade halts and withdrawal freezes happen. In crypto, exchange credit risk and stablecoin depegs can add another layer.
Rules on short selling, market access and taxes vary by country and can change. If an approach depends on a particular platform feature, be aware that exact behaviour differs by provider.
How professionals run arbitrage, and what individuals should know
Professional firms treat arbitrage as an infrastructure game. They invest in low-latency data, co-located servers, multiple clearing relationships and inventory that can be mobilised quickly. They measure every cost, model fair values in real time and size trades so that failed legs do not threaten the firm. Many also act as market makers, which gives them the flow and inventory to hedge efficiently.
Individuals can still apply the mindset on a smaller scale, especially around ETFs, futures basis and obvious exchange-to-exchange gaps. Practical steps include:
- Track all-in costs, not just headline spreads. Include taxes, borrow, funding, FX and transfer fees.
- Use firm orders and test with tiny size first. Partial fills and slippage are common.
- Prefer hedged or simultaneous execution when possible, or use a single venue that lets you trade both legs.
- Be realistic about capital tied up. Margin or inventory needs can be larger than the apparent trade size.
- Keep records of corporate actions, settlement dates and entitlements to avoid surprises.
Arbitrage opportunities tend to shrink as more traders see them. What remains is competed down to a small edge that is earned through better pricing models, faster pipes and tighter operational control. In portfolio language, persistent gains beyond what the market explains show up as alpha, although pure arbitrage aims to keep market exposure close to zero.
In short, arbitrage is about stitching together related prices to extract a small, durable difference. When done with discipline and full cost awareness, it is a craft of details rather than a hunt for big one-off wins.