Enterprise Products Partners (EPD 0.45%), Energy Transfer (ET 0.12%), and MPLX (MPLX 0.17%) are some of the best passive income producers in the energy sector. The trio of master limited partnerships (MLPs) offers big-time yielding payouts that should continue growing in the future.

Their brilliance at producing passive income seems to have caught the market's eye this year as all three have rallied. Here's a look at whether it's too late to buy these income machines.

A milestone year

Units of Enterprise Products Partners have risen more than 10% this year, which is a hefty gain for an income-focused investment vehicle. The valuation increase has pushed the MLP's yield down to around 7.5%. That's still attractive, considering that the dividend yield on the S&P 500 is around 1.5% these days. 

The MLP also still trades at a reasonable valuation. It sells for about 10 times earnings and eight times cash flow. That's dirt cheap compared to the broader market, where the S&P 500 fetches more than 20 times its forward P/E.   

Enterprise Products Partners trades as if it will never grow again, which isn't the case. The MLP is currently in the midst of a major growth wave, with $3.8 billion of expansion projects on track to enter service and start generating cash flow this year. They've given it the fuel to increase its distribution to investors by 5.3% this year. That marked a key milestone for the company as it has now increased its payout for 25 consecutive years. Meanwhile, with another $4.1 billion of projects under construction, it has plenty of fuel to continue growing its earnings and distribution. 

A growth acceleration is ahead

Units of Energy Transfer have gained over 7% on the year. However, even with that rally, the MLP still yields an attractive 9.8%. Further, it trades at a cheap price of only 7.7 times earnings and about 3.9 times cash flow.

The MLP produces plenty of cash to fund its big-time distribution and expansion program. It generated nearly $1.6 billion in cash during the second quarter, covering its distribution with $579 million to spare. It used that excess cash to fund expansion projects ($387 million) and maintain a strong balance sheet.

Energy Transfer's growth should accelerate in the future. The MLP is increasing its capital spending guidance from around $2 billion in 2022 and 2023 to a range of $2 billion to $3 billion in the coming years, fueled by an "incredible backlog of growth opportunities," according to comments by its CFO on the second-quarter call. The company's strong financial profile and growth outlook drive its view that it can increase its distribution at a 3% to 5% annual rate. 

Plenty of fuel to continue increasing its big-time payout

MPLX's unit price has risen about 6% this year. However, the MLP still offers a compelling yield of 8.9%. That's because it trades at a low valuation of 8.8 times earnings and 6.9 times cash flow.

It has produced nearly $2.6 billion in distributable cash through the first half of this year, enough to cover its big-time payout by 1.6 times. That gave it excess cash to fund expansions while maintaining a strong balance sheet. It will also use excess cash to opportunistically repurchase units. 

MPLX currently has several organic growth projects under way. It's expanding its natural gas and natural gas liquids long haul pipelines, crude oil gathering lines, and natural gas processing capacity. These projects should come online over the next two years and supply incremental cash flow. That will give it more money to pay distributions. The MLP has steadily increased its payout since forming a little over a decade ago, including by 10% last year. 

It's still a great time to buy these income-producing machines

While Enterprise Products Partners, Energy Transfer, and MPLX have rallied this year, they remain attractive investment opportunities. The MLPs still trade at relatively bargain valuations, which is why they offer such high-yielding payouts. They're great options for investors seeking attractive ways to generate passive income.