As investors constantly search out the latest, greatest dividend-yielding securities, it was only a matter of time until they got to Master Limited Partnerships, or MLPs. MLPs are most oil and gas infrastructure companies that are structured as ... as the name suggests ... partnerships. That structure means that they pass essentially all of their income down to shareholders, in the form of high dividends; the corporations are exempt from taxation. These MLPs have been a hot topic recently: A report from Standard and Poor's says that the number of energy-related MLPs is up 150% over the past six years.

Looking to capitalize on investor interest, S&P recently unveiled an index tracking the space. Potential components must also have market capitalization of at least $300 million and a three-month average daily trading value of at least $2 million. Currently, 40 companies make the grade, and components are capped at 15% of the index. Through July 13, the index was up 17.37% year-to-date, and had an impressive 21.73% five-year annualized return.

This index seems destined ... and, indeed, designed ... to serve as the underlying one for investable products. Toward that end, however, S&P has been beaten to the punch ... by itself. S&P actually calculates another MLP index for Alerian Capital Management, and that index was recently licensed by Bear Stearns to underlie a recently launched exchange-traded note (ETN), the BearLinx Alerian MLP Select Index ETN, which trades on the NYSE under the symbol BSR and carries an annual expense ratio of 0.85%.