 (In some markets, a leg that is purchased is mentioned before a leg that is sold and commonly the more expensive leg is also mentioned first (to avoid using a negative spread price).Therefore, the way that the CAISO box spread is referred to suggests that SP is trading over NP, and SP-minus-NP is wider in 2013 than in 2012).Another pair of contracts that commonly trade box spreads are WTI and Brent crude oil, either in the form of intra-commodity calendar spreads for WTI and Brent using the same calendar expirations for each or different expiration WTI/Brent inter-commodity spreads.