The investment seeks investment results that correspond generally to the price and yield (before the fund's fees and expenses) of an equity index called the ISE-Revere Natural Gas? Index. The fund will normally invest at least 90% of its net assets (including investment borrowings) in the common stocks, depositary receipts and MLP units that comprise the index. The index is designed to track the performance of mid and large capitalization companies that derive a substantial portion of their revenues from midstream activities and/or the exploration and production of natural gas.