A stock option is a specific type of option with a stock as the underlying instrument (the security that the value of the option is based on). Thus it is a contract to buy (known as a "call" contract) or sell (known as a "put" contract) shares of stock, at a predetermined or calculable (from a formula in the contract) price.

Valuation

A stock option contract's value is determined by five principal factors:-

• The price of the stock,
• The strike price,
• The cumulative cost required to hold a position in the stock (including interest + dividends),
• The time to expiration,
• The estimate of the future volatility of the stock price.

For large corporations in economies such as the United States, there is a liquid market in european put and call stock options for certain expiry dates and certain strikes close to the current stock price. Thus for those contracts valuation is given "by the market". For other contracts, with different strikes and different expiries the market price can be used to give an estimate of the future volatility, which in turn can be used in models such as the binomial options model (for American options) or the Black-Scholes model with volatility smile for European options to value the non-standard contracts.

Trading

Options themselves are traded as securities. The most common way is trading standardized options contracts that are listed by various exchanges -- there are currently six options exchanges in the United States that list standardized options contracts based on underlying stocks.

There are also "over the counter" options contracts that are traded not on exchanges, but between two independent parties. At least one of those parties is usually a large financial institution with a balance sheet big enough to underwrite such a contract.

Options trading, without intent to ever exercise the option, can be used as a form of leverage. The price of an option on a security will move more than the price of the security itself. For this reason and due to their usefulness in financial engineering, the total value of trading in options has at times exceeded the total value of trading in stocks themselves.

Employee Stock Options

Main article: Employee stock option

Stock options for the company's own stock are often offered to upper-level employees as part of the executive compensation package, especially by American business corporations. It is also sometimes done for non-executive employees, especially in the technology sector, in order to give all employees an incentive to help the company become more profitable. For details see the employee stock option article.

See also

• List of finance topics
• Derivative markets
  • Derivative security
    • Bond options
    • Credit derivatives
    • Foreign exchange options
    • Interest rate options
    • Warrant

External links

• The Open Site Encyclopedia section on Options
• Shares and share unlike - 1999 article from The Economist questioning whether investors (as owners) actually gain from large option packages for top management.