Dividend stocks can be great long-term investments. Companies that pay a dividend have historically outperformed the S&P 500 with a lot less volatility. The best returns, however, have often come from those that consistently increased their dividends. They've not only outperformed nonpayers but also those that just maintained their payout.

Because of that, investors looking for a great dividend stock need to seek out the ones that can routinely increase their payout. Here's a look at pipeline giant ONEOK's (NYSE:OKE) dividend growth history and outlook.

A jar of coins with the word dividends written on the front.

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A solid dividend history

ONEOK has been an excellent income stock, delivering more than 25 years of dividend stability and growth. While the company hasn't increased its payout every single year, it has boosted it quite often, raising it in most quarters.

After keeping its payout flat through all of 2016 and into much of 2017, the company has now reeled off eight consecutive quarterly increases. Overall, it has boosted it by 9% over the past year, pushing the current yield up to 5.1%.

The current payout level is on pretty solid ground. ONEOK has generated $1.5 billion in cash through the third quarter, which has covered its dividend by a comfortable 1.42 times. Meanwhile, its leverage ratio stood at 4.5 times debt-to-EBITDA at the end of the third quarter. While that's above its sub-4.0 target, the company sees leverage getting back into its comfort zone by the end of next year as it completes its current expansion projects.

Plenty of fuel to keep growing

Those projects have the company on track for accelerated earnings growth in 2020. ONEOK currently expects its EBITDA to rise by about 6% this year before increasing at a greater than 20% rate in 2020. That's because it has five expansions coming on line by the first quarter of next year, totaling $4.5 billion of investment.

Meanwhile, it has another expansion wave coming in the first quarter of 2021. At the moment, seven projects totaling $1.85 billion should enter service in the late 2020 to early 2021 time frame. Because of that, earnings should continue growing at a high rate over the next couple of years as volumes across these systems ramp up.

That will provide ONEOK with a growing stream of cash flow that should help bolster its financial profile. As noted, leverage should drop below its target level by the end of next year. Meanwhile, dividend coverage should further improve.

Because of that, ONEOK should be able to continue increasing its payout for the next few years. In the company's view, it should be able to grow it at a 9% to 11% annual rate through at least 2021. That's a well-above-average growth rate. For comparison, analysts currently expect the median dividend stock in the S&P 500 with a similar payout history as ONEOK to deliver annual growth of about 5.3% per year during that time frame.

A great stock for income seekers

While ONEOK hasn't increased its dividend every year, it has given its investors a raise in most of the last 25 years. Even better, when the company is growing its payout, it typically does so every quarter. That growth trend looks like it will continue for at least the next few years, given the company's upcoming waves of expansion project start-ups. Because of that, ONEOK looks like a great stock for dividend investors.