In finance, a foreign exchange option (commonly shortened to just FX option or currency option) is a derivative financial instrument where the owner has the right but not the obligation to exchange money denominated in one currency into another currency at a pre-agreed exchange rate on a specified date; see Foreign exchange derivative.

The FX options market is the deepest, largest and most liquid market for options of any kind in the world. Most of the FX option volume is traded OTC and is lightly regulated, but a fraction is traded on exchanges like the International Securities Exchange, Philadelphia Stock Exchange, or the Chicago Mercantile Exchange for options on futures contracts. The global market for exchange-traded currency options was notionally valued by the Bank for International Settlements at $158,300 billion in 2005.

For example a GBPUSD FX option might be specified by a contract giving the owner the right but not the obligation to sell £1,000,000 and buy $2,000,000 on December 31. In this case the pre-agreed exchange rate, or strike price, is 2.0000 USD per GBP (or 0.5000 GBP per USD) and the notionals are £1,000,000 and $2,000,000.

This type of contract is both a call on dollars and a put on sterling, and is often called a GBPUSD put by market participants, as it is a put on the exchange rate; it could equally be called a USDGBP call, but market convention is quote GBPUSD (USD per GBP).

If the rate is lower than 2.0000 come December 31 (say at 1.9000), meaning that the dollar is stronger and the pound is weaker, then the option will be exercised, allowing the owner to sell GBP at 2.0000 and immediately buy it back in the spot market at 1.9000, making a profit of (2.0000 GBPUSD – 1.9000 GBPUSD)*1,000,000 GBP = 100,000 USD in the process. If they immediately exchange their profit into GBP this amounts to 100,000/1.9000 = 52,631.58 GBP.

The factors affecting XXX will affect both XXXYYY and XXXZZZ. This causes positive currency correlation between XXXYYY and XXXZZZ.

On the spot market, according to the BIS study, the most heavily traded products were:

* EURUSD: 27%
* USDJPY: 13%
* GBPUSD (also called cable): 12%

and the US currency was involved in 86.3% of transactions, followed by the euro (37.0%), the yen (17.0%), and sterling (15.0%) (see table). Volume percentages for all individual currencies should add up to 200%, as each transaction involves two currencies.

Trading in the euro has grown considerably since the currency’s creation in January 1999, and how long the foreign exchange market will remain dollar-centered is open to debate. Until recently, trading the euro versus a non-European currency ZZZ would have usually involved two trades: EURUSD and USDZZZ. The exception to this is EURJPY, which is an established traded currency pair in the interbank spot market. As the dollar’s value has eroded during 2008, interest in using the euro as reference currency for prices in commodities (such as oil), as well as a larger component of foreign reserves by banks, has increased dramatically. Transactions in the currencies of commodity-producing countries, such as AUD, NZD, CAD, have also increased.