The energy market has been red-hot over the past year thanks in part to rising oil prices, which have helped drive the average energy company in the S&P 500 up about 20%.

However, that rising tide hasn't lifted all boats. Two energy stocks that have fallen behind are pipeline giants Kinder Morgan (NYSE:KMI) and Enbridge (NYSE:ENB), which have declined 6% and 12%, respectively, over that time frame. Because of that, these high-yielding dividend stocks now trade at dirt-cheap valuations, making them great options to consider buying now.

A dividend on solid ground

Kinder Morgan currently expects to generate about $2.05 per share in free cash flow this year, which would be about 4% higher than last year and less than 5% from its peak a few years ago. With shares currently trading for around $18, it implies that the stock sells for less than nine times cash flow. That's well below its peer-group average of 12.5 times cash flow -- at the bottom of the group, in fact.

A neon sign with the word "sale."

Image source: Getty Images.

That low valuation doesn't make any sense given what Kinder Morgan has coming down the pipeline. The company recently agreed to sell its highly controversial Trans Mountain Pipeline expansion to the Government of Canada, and it will receive a boatload of cash that it intends on using to repay debt. That will further firm up the company's balance sheet, which has gone from a liability to an asset over the past few years.

Meanwhile, the company has added new growth projects by securing one large-scale natural gas pipeline out of the fast-growing Permian Basin while making headway on another one. The combination of the company's rapidly improving balance sheet and increasing opportunity for future growth puts its 4.5%-yielding dividend on solid ground, making it more and more likely that Kinder Morgan can realize its plan to boost the payout another 25% in both 2019 and 2020.

A high-yield for a low price

Enbridge estimates that it can produce about $3.33 per share in free cash flow this year, which represents a roughly 15% increase from 2017. With shares of the Canadian pipeline giant currently selling for around $35, it implies a valuation of roughly 10.5 times cash flow -- which, like Kinder Morgan, puts it well below the 12.5 average of its peer group.

And as with Kinder Morgan, that valuation disconnect also doesn't make much sense. Enbridge currently has a massive expansion program underway that should grow cash flow per share at a 10% compound annual growth rate through 2020. And that would support a similar growth rate in the company's high-yielding dividend.

Meanwhile, the company has recently strengthened its balance sheet by selling several noncore assets, which will enable it to hit its targeted leverage ratio. On top of that, it's in the process of simplifying its corporate structure by working to acquire all its publicly traded affiliates. Add it all up, and Enbridge's 5.9%-yielding dividend is on an increasingly solid footing, which raises the likelihood that the company can grow the payout at a double-digit annual pace over the next few years. Combine that fast-growing high-yield dividend with a very cheap valuation, and Enbridge is an excellent stock to buy these days.

The market has made a mistake

Kinder Morgan and Enbridge have significantly underperformed other energy stocks over the past year even though their financials are improving. Because of that, investors have a chance to scoop up these dividend payers at fantastic prices. Those factors position buyers to collect a lucrative income stream, and generate potentially outsized returns as their valuations eventually move closer to the peer group average. Income with that much upside is hard to find, which is why these two pipeline stocks appear to be great to consider buying right now.

Matthew DiLallo owns shares of Enbridge and Kinder Morgan. The Motley Fool owns shares of and recommends Kinder Morgan. The Motley Fool recommends Enbridge. The Motley Fool has a disclosure policy.