The index consists of MLPs involved in oil exploration and production, natural gas exploration and production, the sale, distribution and retail marketing of propane and other natural gas liquids, crude oil shipping, dry bulk shipping, refined products transportation, liquefied natural gas shipping, other marine transportation, and the direct mining, production and marketing of natural resources, including timber, fertilizers, coal and other minerals, and royalty trusts, which typically own the rights to royalties on the production and sales of a natural resource, including oil, gas, minerals and timber.