If you need income from your investment portfolio, you're not alone. Millions of investors have struggled in recent years to find income-producing assets in an environment in which ordinary fixed-income securities like bonds have had thoroughly inadequate yields. In order to make ends meet, investors have had to research new areas of the market to find enough income.

In this week-long look at various types of income investments, we looked yesterday at mortgage REITs and the double-digit yields they offer. But mortgage REITs aren't the only option for income-hungry investors. Master limited partnerships also produce substantial distributions for investors, and unlike most mortgage-REIT dividends, some MLP payouts have amazing tax benefits. Let's take a closer look at MLPs with the goal of getting more familiar with the way they work and the opportunities and risks involved.

Making your portfolio energetic
Master limited partnerships are publicly traded business entities that focus on the natural resources industry. In particular, many midstream oil and gas businesses that use pipelines and storage facilities to transport and store energy products take advantage of the MLP structure, which allows the business to avoid the corporate taxation that most regular corporations pay. The resulting tax savings gets passed on to MLP unitholders in the form of extra income, and MLPs typically pay out most or all of their income to their investors through sizable regular distributions.

Another benefit for MLP investors is that the distributions the MLP makes are often at least partially tax-free. With MLPs qualifying for special deductions like depletion allowances, substantial portions of what you receive may not count as taxable income.

MLPs do come with some complexity for investors, though. Partnership taxation is beneficial for the business entity, but it brings complications to unitholders, who have to report their proportional share of business income on their tax returns as shown on K-1 partnership tax statements. These statements are often far more complex than the tax forms you get from ordinary stocks and can require accounting help and the attendant cost.

What kinds of MLPs are available?
Pipeline businesses are the most common MLPs, with numerous examples of entities that pay impressive dividends. Energy Transfer Partners (ETP) has multiple gas pipelines totaling more than 20,000 miles across the U.S., with its most substantial presence in Texas. Currently paying an 8% distribution yield to unitholders, Energy Transfer Partners has made several growth moves recently, including its acquisition of Sunoco to help it diversify into oil pipelines.

But you can find MLPs in other industries. Take these examples:

  • Ferrellgas (FGP) is an MLP that distributes propane for household and commercial use, with its best-known product being its Blue Rhino refillable gas tanks. It has a current dividend yield of more than 11%.
  • Fertilizer MLPs have become hugely popular, thanks to big demand for crop-yield-enhancing products for farming. Terra Nitrogen (NYSE: TNH) and Rentech Nitrogen Partners (NYSE: RNF) sport yields of 8% to 9% and have also experienced substantial growth, as relatively low costs of the natural gas needed to produce nitrogen-based fertilizers has reduced overall expenses and boosted margins.
  • Alliance Resource Partners (ARLP 0.47%) is an MLP that specializes in coal production. The coal business has been depressed due to a lack of demand as many users, especially electric-generating utilities, have turned to cheap natural gas as an alternative fuel source. But despite depressed prices, Alliance has still maintained an attractive dividend yield of around 8%.

As you can see, MLPs come in all shapes and sizes. Although they have the natural-resource thread in common, you can get many different types of natural-resource exposure using the MLP framework.

Risks
MLPs aren't without risk. As operating businesses, they're subject to the same risks that non-MLP players in their respective industries face. For instance, for midstream MLPs, pipeline volumes aren't entirely dependent on energy prices, but producers tend to cut back on drilling and pumping activity when prices are low, which can then reduce revenue for MLPs.

More broadly, some policymakers have targeted MLPs as prospects for tax reform. With the fiscal cliff leading to negotiations aimed at eliminating tax loopholes, MLP tax benefits could potentially be eliminated or reduced for at least some investors in higher tax brackets.

Where else will you find income?
MLPs are definitely worth a close look for income-seeking investors, but if you're not excited about the prospects for energy and other natural resources, they may not be the right answer for you. So where else can you find the income you need? Stay tuned tomorrow as I take a closer look at another income-rich area of the market: dividend ETFs.