During times when the stock market is a roller-coaster ride for investors, dividends can add a steady stream of income to offset bumps in a portfolio. And right now, investors can find some impressive dividend yields in pipeline stocks.

These companies, which provide the means for transporting oil and gas from wellhead to refineries, are considered to be the toll roads of the energy infrastructure. And because they earn fees that aren’t dependent on energy prices and enjoy consistent demand for their services even when the economy slows, many pipeline stocks can produce steady cash flow and pay generous dividends.

Three high-yielding pipeline stocks are catching my attention right now, because they’re making big investments that will be a strong catalyst for future distribution growth. The fact that they already yield more than 6% makes them particularly enticing for any income portfolio. Here they are…

1. NuStar Energy LP (NYSE: NS)
Yield: 8%
A spin-off from Valero Energy (NYSE: VLO), which focuses on oil refining, NuStar owns crude-oil terminals and storage facilities, 8,400 miles of pipeline and two asphalt refineries. The company is the world’s fourth-largest independent terminal operator in the United States and a leading asphalt producer. In recent years, NuStar has consolidated operations, made accretive acquisitions and improved its balance sheet to investment grade. The company has been paying distributions since 2001 and has increased payments nine years in a row.

The company’s latest financials are solid. NuStar improved EBITDA by 6% in the first nine months of 2011 to $391.7 million compared with a year earlier, while increasing distributable cash flow per unit by 11% to $3.79. For the full year, however, the company expects EBITDA to be flat because of a temporary shutdown of a customer’s refinery.

The good news is that Nustar should begin reaping the benefits of nearly $500 million invested in facility upgrades and expansion later this year. The company is expanding a major terminal serving the Bakken oilfield, adding capacity to a pipeline serving the Eagle Ford Shale project and connecting other Mid-Continent oil fields to its system.

The fact that insiders recently purchased $10 million of the stock signals their confidence in NuStar’s future. Shareholders will likely benefit from improved 2012 income and collect 8% while they wait.

2. Atlas Pipeline Partners (NYSE: APL)
Yield: 6%
Atlas operates five gas-processing plants and 8,600 miles of pipeline in the Mid-Continent region (Oklahoma, Kansas and Texas). The company also holds a 20% stake in a West Texas liquid natural gas (LNG) pipeline majority-owned by Chevron (NYSE: CVX).

Atlas facilities are currently operating at maximum throughput, which is the reason the company is spending more than $600 million to double production capacity. Atlas is expanding its western Oklahoma gas-gathering system, upgrading a west Texas processing facility (the second expansion of this facility in 18 months), and greatly increasing transportation capacity of its Velma system that serves Woodford Shale gas fields.

The great thing is that Atlas is funding these upgrades without resorting to dilutive equity offerings. The company paid down nearly $700 million of debt in 2011 using proceeds from an asset sale and has ample borrowing capacity, with debt now totaling just one-third of equity.

The balance sheet is also incredibly solid. During the first nine months of 2011, Atlas generated EBITDA of $131.8 million. The expansion projects, once completed, are expected to add another $150 million to annual EBITDA. In the same period, Atlas boosted distributable cash flow by 45% to $93.9 million compared with a year earlier, and hiked distributions 15% in the third quarter. This marked two consecutive quarters of double-digit distribution growth and more than 50% growth in the distribution year-to-date.

3. Cheniere Energy Partners LP (AMEX: CQP)
Yield: 9%
Cheniere owns the Sabine Pass LNG terminal in Louisiana, where it’s developing an LNG processing plant intended for import and export. The company has secured the necessary permits and plans to begin construction on the plant in early 2012, with operations scheduled to commence in 2015.

At first glance, the stock doesn’t appear too attractive. Under a heavy $2.2 billion debt load, Cheniere has been struggling for years and, because of development costs for the new plant, it registered a weakened operating income in the first nine months of 2011 — $50.4 million compared with the $78.1 million generated a year earlier.

But Cheniere’s fortunes are on the verge of improving rapidly. The company has recently signed three multi-billion dollar contracts for LNG production from the new plant: a 20-year, $8 billion contract to supply LNG to UK-based BG Group; a 20-year, $9 billion contract with Spain’s Gas Natural Fensoa; and a 20-year contract of undisclosed value with India’s state-run energy company Gail India. All this is great news for shareholders, since the contracts could add at least $410 million annually to the company’s coffers and enable growth in a dividend that hasn’t been raised since 2007.

BG Group predicts demand for LNG exports from the United States will triple in the next few years, so there should be no lack of customers for Cheniere LNG exports. The annual production capacity of the new LNG plant is designed to exceed 9 million tons.

Risks to consider: Cheniere is raising $300 million through an equity offering, but will likely be making multiple unit offerings in the next three years to fund construction of its new plant. These offerings will dilute the ownership of existing unit holders.

Action to take –> Cheniere has the highest dividend, but is the most risky of the three pipeline companies, since its growth prospects depend on a yet-to-be-built plant. Of the three, my top pick is Atlas, because of its distribution growth and ability to fund expansion organically. If the construction sector strengthens, then NuStar becomes more attractive as demand for asphalt improves. At present, NuStar’s asphalt operations are a drag on earnings.