Exchange traded funds that follow master limited partnerships have outperformed the S&P 500 this year and attracted the attention of investors starved for income. More MLP ETFs are in the works so investors will have more choice, but they need to put in the research and understand the subtle differences between funds that track this popular asset class.

MLP exchange traded products have gained as much as 14% over the year and provided yields of over 5%, compared to the 2.7% year-to-date increase in the S&P 500.

MLPs are a type of limited partnership that is publicly traded like a stock. As a limited partner, the individual or group that provides capital to the MLP is entitled to periodic income distributions. MLPs are required to generate around 90% of their cash flow from real estate, natural resources or commodities. [Master Limited Partnership ETFs]

Most MLP funds follow companies that transport, store, process, refine, market and mine natural resources, such as oil or natural gas. As such, growth and revenue is less dependent on the actual price of the commodity, but more on how much volume is being moved.

According to Abraham Bailin, a Morningstar analyss, individuals who invest in MLPs believe that “the country’s basic infrastructure requires further investment, these companies will continue to be able to tap capital markets effectively, fuel demand will stabilize or start growing going forward, and interest rates will not dramatically increase.”

JP Morgan Alerian MLP Index ETN (NYSEArca: AMJ) is an exchange traded note that tries to reflect the performance of midstream energy MLPs that gather, process, transport and store crude oil or natural gas. AMJ has an expense ratio of 0.85%. The fund offers a yield of 5.2% and is up 11.9% year-to-date.

Credit Suisse Cushing 30 MLP Index ETN (NYSEArca: MLPN) tries to reflect the performance of the Cushing 30 MLP Index, which tracks mid-stream energy infrastructure assets in North America. The ETN has an expense ratio of 0.85%. MLPN yields 5.4% and has gained 8.9% year-to-date.

UBS E-TRACS Alerian MLP Infrastrctr ETN (NYSEArca: MLPI) tries to reflect the Alerian MLP Infrastructure Index, which includes 25 energy infrastructure MLPs. The ETN has an expense ratio of 0.85%. MLPI yields 5.0% and has increased 14.4% year-to-date.

It should be noted that as ETNs, these funds are subject to the credit worthiness of the issuing bank, which include JP Morgan (NYSE: JPM), Credit Suisse (NYSE: CS) and UBS (NYSE: UBS), respectively.

ALPS Alerian MLP ETF (NYSEArca: AMLP) tries to reflect the performance of the Alerian MLP Infrastructure Index. The ETF also has an expense ratio of 0.85%. AMLP offers a 6.3% yield and has performed 9.2% year-to-date.

According to a recent Securities and Exchange Commission exemptive relief filing, Exchange Traded Concepts will help money managers  Yorkville ETF Advisors market the new Yorkville High Income MLP ETF. The new fund will invest in MLPs engaged in oil exploration and production, natural gas exploration and production; the sale, marketing, extraction and transportation of other resources.

JP Morgan Alerian MLP Index ETN

For more information on master limited partnerships, visit our MLPs category.

Max Chen contributed to this article.