ADR Arbitrage and the Conversion Mechanism

A US investor who wants to own shares of a company listed only in Tokyo or São Paulo faces a real headache: opening a foreign brokerage account, dealing with a foreign currency, and navigating unfamiliar settlement rules. An American Depositary Receipt (ADR) solves this by trading a US-dollar-denominated certificate, on a US exchange, during US market hours, where each certificate represents a claim on a specific number of the actual foreign shares, held in custody overseas. The mechanism that keeps the ADR's dollar price honest relative to the foreign share's local price is what makes ADR arbitrage possible.

How the certificate is built

A depositary bank (commonly JPMorgan, BNY Mellon, Citibank or Deutsche Bank) holds the actual foreign shares in a vault, through a local custodian bank in the company's home market, and issues ADRs against them in the US. Each ADR has a fixed ratio to the underlying local share — for instance, "1 ADR = 2 ordinary shares," or, just as often, a fraction, "1 ADR = 0.5 ordinary shares," chosen mainly so the ADR's dollar price lands in a familiar trading range for US investors.

The link between the two prices is direct: an ADR's fair value is the local share price, converted to US dollars at the prevailing exchange rate, multiplied by the ratio. If the local share trades and the ADR trades far from that relationship, an arbitrage opens up — and the depositary bank's creation and redemption process is what an arbitrageur uses to close it.

Creation: an arbitrageur (typically an authorized broker-dealer) buys the underlying shares in the local market, delivers them to the local custodian, and the depositary bank issues new ADRs in exchange, which the arbitrageur then sells in the US. This happens when the ADR trades rich (above fair value) — sell expensive ADRs, buy cheap local shares to back them.

Redemption runs the reverse: buy ADRs (cheap), deliver them to the depositary bank, receive the underlying local shares, and sell those shares in the local market. This happens when the ADR trades cheap relative to the local shares.

A worked example

A company's local shares trade in Seoul at ₩50,000. The ADR ratio is 1 ADR = 0.25 shares, and the won trades at 1,300 per US dollar. Fair value for the ADR is: convert one full local share to dollars, $50{,}000 / 1{,}300 = 38.46$, i.e. $38.46, then apply the ratio, $38.46 \times 0.25 = 9.62$, i.e. $9.62. Suppose the ADR is actually trading at $9.90 in New York — it is rich by about 2.9%.

An arbitrageur buys 4 local shares in Seoul for $4 \times 50{,}000 = 200{,}000$ won (roughly $153.85 at the same exchange rate), deposits them with the custodian, and receives $4 / 0.25 = 16$ ADRs, which it sells in New York at $9.90 each for $16 \times 9.90 = 158.40$, i.e. $158.40. The gross profit is $158.40 - 153.85 = 4.55$, i.e. $4.55 on the trade — about 3% of the notional, before transaction costs, FX costs and the depositary bank's own conversion fee, which typically runs a few cents per ADR and is usually the deciding factor in whether the trade clears a profit at all.

Why the gap doesn't stay open long

In liquid ADR programs on major developed-market names, the gap between the ADR and its fair value rarely exceeds a few basis points for more than a few minutes, because dozens of desks run this exact conversion trade continuously and the local and US markets overlap enough in trading hours to keep both legs live at once. The gap widens, and stays open longer, in three situations: thinly-traded local shares where the arbitrageur's own buying moves the local price before the position is fully built; time-zone mismatches, where the local market is closed while the ADR trades in New York, so the "local" price used for fair value is stale; and, as above, any restriction on new creation or redemption that breaks the physical link between the two markets.

• FX risk sits inside the arbitrage, not outside it. The local leg and US leg settle in different currencies at different times; a currency move between trade and settlement eats directly into the spread.
• Not all depositary receipts are backed 1:1 by fresh deposits at all times — "unsponsored" ADRs, created by a bank without the foreign company's involvement, can have thinner, less reliable conversion mechanics.
• Dividends pass through, minus a cut. The depositary bank converts foreign dividends to dollars and typically deducts a small custody fee before paying ADR holders — check the fee schedule, not just the headline yield.