MPLX (NYSE:MPLX) has lost more than 20% of its value in the last year. That slump is a bit of a head-scratcher, because the master limited partnership's cash flow per unit increased by more than 10% through the first six months of 2019 compared to the year-ago period. As a result, the company's valuation is at a bargain-basement level.

Further, with its unit price slumping, its dividend yield has risen to 9.4%, thanks also to a 6.4% increase in its payout over the past year. The combination of all those factors makes MPLX one of the more attractive income investment opportunities available right now.

A roll of cash next to a calculator and a sticky note with the word dividends.

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A top-notch payout

Usually, when a dividend yield is around 10%, it's due to concerns about its sustainability. However, that's not the case with MPLX. For starters, the company produces very predictable cash flow backed primarily by fee-based contracts. Further, it has generated enough cash to cover its payout by 1.38 times so far this year, which is well above its 1.2 comfort level. The company adds even more support to its payout by having a solid investment-grade balance sheet that it backs with a conservative 3.9 leverage ratio. That's right below its 4.0 target. Because of those solid metrics, MPLX has the financial flexibility to fund its expansion projects.

Visible growth for the next few years

MPLX recently bolstered its growth prospects by acquiring affiliated MLP Andeavor Logistics. That transaction diversified its portfolio while enhancing its footprint in the fast-growing Permian Basin. Because of that, the combined company has the scale and asset base to build out integrated systems to gather, store, process, transport, and export natural gas, natural gas liquids (NGLs), and oil from that region.

On the natural gas side, the company is building three new processing plants in the Permian that will feed gas and raw NGLs into pipelines it has under development. The Whistler Pipeline will move the gas toward Texas' coast. Meanwhile, BANGL will ship NGLs in that same direction to a fractionation hub it's developing, which will separate them into pure products like ethane and propane. The company expects to finish both large-scale pipelines by 2021.

On the oil side, MPLX is expanding Andeavor's legacy oil gathering business in the Permian. It's also leveraging that system to pursue additional expansion opportunities further downstream. For example, it's investing in the Wink-to-Webster pipeline, which will move crude oil from the Permian to the Gulf Coast when it starts up in 2021. The company is also expanding its recently acquired Mt. Airy terminal, which will enable it to export more oil and refined products. That's one of several export projects it's working on as it seeks to take advantage of increased oil flows to the Gulf Coast.

These projects position MPLX to grow its cash flow at a healthy pace over the next few years. That should enable it to continue increasing its distribution to investors.

A bottom-of-the-barrel valuation

Typically, when a company pays a well-supported and growing dividend and has visible expansion prospects, it trades at a premium valuation. However, that's not the case with MPLX.

The company is currently on track to generate about $3.66 per unit of cash flow for 2019. However, with units recently trading at around $28.50 apiece, it implies that MPLX sells for less than eight times cash flow. That's dirt cheap considering that most of its midstream peers fetch at least 10 times their cash flow.

A dirt cheap income stream

Units of MPLX have sold off in the past year, which doesn't make much sense, especially since its recent merger with Andeavor Logistics enhanced its growth prospects without negatively affecting its ability to continue increasing its high-yield dividend. Now the company's sell-off looks like a great buying opportunity, since investors are getting not only a much cheaper price but also a higher yield. That sets dividend investors up to earn an even better total return in the coming years.