The price of natural gas has tumbled 30% this year due to an overabundance of supply. That has weighed on energy stocks focused on this fossil fuel. The sector's slump has even affected businesses that don't have much direct exposure to gas prices, like midstream companies. Three of the biggest underperformers have been Energy Transfer (NYSE:ET), MPLX (NYSE:MPLX), and Williams Companies (NYSE:WMB).

However, since they don't have much direct exposure to gas prices, all three of these pipeline companies are on track to produce record earnings. As such, they're much more attractive values right now, making them among the top stocks to buy in the sector.

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A record year with nothing to show for it

Energy Transfer has lost about 9% of its value this year. While the master limited partnership (MLP) is one of the largest natural gas pipeline companies in the country, it doesn't have much direct exposure to commodity prices. That's because fee-based contracts supply between 85% to 90% of its annual earnings, which provides it with very steady cash flow.

Instead of falling along with gas prices, Energy Transfer's earnings are on track to rise to a record $11 billion this year. That would put them about 16% above 2018's total, which is better than its initial view that they'd increase by about 12.6% this year. Fueling that growth is the recent completion of several large-scale expansion projects.

With its earnings rising even as its unit price has declined, Energy Transfer's valuation has fallen to an insanely cheap level. Meanwhile, its dividend yield has risen above 10%. Add that income and value to the growth it sees ahead in 2020, and Energy Transfer is about as attractive an investment option as investors will find in the energy patch.

Making all the right moves

MPLX has slumped about 17% this year, due in part to its large natural gas gathering and processing business. However, while the MLP has lots of exposure to the gas sector, that hasn't had any impact on its cash flow. It has generated just over $3 billion in cash flow through the third quarter, up 47% year over year, due in part to the acquisition of an affiliated MLP.

MPLX has used its growing cash flow to continue increasing its distribution to investors. Overall, it has boosted it by 6.3% over the past year. Combine that with its declining unit price, and the yield is up to 10.8%.

While a dividend yield in the double digits is usually a sign of trouble, that's not the case with MPLX since it can currently cover it with cash flow by 1.5 times. Further, it has a solid balance sheet backed by a conservative leverage ratio. Add those factors to the expectation that the company will continue growing at a healthy rate in 2020 and beyond, and it's a great buy this month.

Pipelines heading towards the bright sun.

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Still growing strong

While Williams Companies' shares have gained about 5% this year, they're about 20% below their recent high and have significantly underperformed the S&P 500. This lackluster performance comes even though the natural gas pipeline giant is on track for an excellent year. Overall, it expects to haul in $3.1 billion in cash, which would be about 8% ahead of last year's level. Because of that, the company had the fuel to increase its dividend by another 12% -- boosting the yield up to its current level of 6.6% -- while maintaining a conservative 60% payout ratio.

Weak natural gas prices, however, will have a slight impact on Williams' growth rate in 2020 as it will slow to about 5% because it won't be connecting as many new gas wells to its system next year. However, that's right in line with its long-term outlook that cash flow will grow by 5% to 7% per year. Further, it will give it the fuel to boost its dividend by another 5% in 2020. That visible growth makes Williams an ideal stock for investors who want a steadily rising income stream

Great all-around values these days

Slumping gas prices have weighed on gas pipeline companies this year, even though they have limited direct exposure to pricing. Because of that, investors can buy these energy stocks at cheaper valuations today since all three grew their earnings even as their stock prices underperformed. Add in their above-average yields, and this trio of energy stocks could fuel big-time total returns from here, making them great buys right now.