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In finance, a spread option is a type of option where the payoff is based on the difference in price between two underlying assets. For example the two assets could be crude oil and heating oil; trading such an option might be of interest to oil refineries, whose profits are a function of the difference between these two prices. Spread options are generally traded over the counter, rather than on exchange.〔(Global Derivatives: Spread option )〕〔(Investopedia:Spread option )〕 A 'spread option' is not the same as an 'option spread'. A spread option is a new, relatively rare type of exotic option on two underlyings, while an option spread is a combination trade: the purchase of one (vanilla) option and the sale of another option on the same underlying. ==Spread option valuation== For a spread call, the payoff can be written as where S1 and S2 are the prices of the two assets and K is a constant called the strike price. For a spread put it is . When K equals zero a spread option is the same as an option to exchange one asset for another. An explicit solution, Margrabe's formula, is available in this case. In 1995 Kirk's Approximation,〔Kirk E. (1995); Correlation in the Energy Markets, in: Managing Energy Price Risk, Risk Publications and Enron, London, pp. 71–78〕 a formula valid when K is small but non-zero was published. This amounts to a modification of the standard Black-Scholes formula, with a special expression for the sigma (volatility) to be used, which is based on the volatilities and the correlation of the two assets. The same year Pearson published an algorithm〔(N. Pearson: An efficient approach for pricing spread options )〕 requiring a single numerical integration to compute the option value. This method was improved upon in 2006 when Li, Deng and Zhou〔Li, Deng and Zhou: Closed-Form Approximations for Spread Option Prices and Greeks ()〕 published accurate approximation formulas for both spread option prices and their Greeks. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Spread option」の詳細全文を読む スポンサード リンク
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