A lot of investors have energy on the brain. Tracking oil prices rivals monitoring the daily activities of the Kardashians as the national pastime (personally, I find oil prices more interesting).

The recent rally in oil, oil stocks and master limited partnerships (MLPs) has given a bit of relief to battered investors who’ve endured a sharp drop in prices over the past few months.

One of those MLPs is NuStar Energy (NYSE: NS), a San Antonio-based company that transports and stores petroleum products.

NuStar is typical of many MLPs in that it operates pipelines and storage facilities. Since it is not an oil driller, it is not as dependent on the price of oil as oil producers, like Exxon Mobil (NYSE: XOM).

Most pipeline and storage MLPs collect fees for transporting and storing oil and gas. They act as a sort of toll taker on their pipelines. Once the pipeline is built, it’s a very high-margin business.

MLPs also return most of their distributable cash flow (DCF) back to shareholders in the form of dividends, which MLPs call distributions.

NuStar has paid unit holders (MLP investors are called unit holders, not shareholders) $1.095 per unit each quarter since August 2011. It has paid a distribution since 2001. The distribution steadily rose until it was frozen in 2012.

The company will report third quarter results on November 3. For the first half of the year, DCF was $2.55 per share, more than covering the $2.19 per share in distributions that unit holders received.

But that’s misleading.

Remember, unit holders are limited partners. There is also a general partner, called NuStar GP Holdings (NYSE: NSH), which owns a 2% general partner interest and 12.9% of the limited partner interest. The general partner receives an incentive distribution that has come out to about $50 million per year the past two years.

If you include the general partner incentive, NuStar’s cash flow does not cover the full amount of the distribution.

Considering that the distributions per share and the total amount of distributions have been very consistent over the past 2 1/2 years, it concerns me that once again the company won’t generate enough cash flow to cover the distribution payments.

In 2013 and 2014, NuStar Energy paid $392 million in distributions, including those made to the general partner. It’s on pace for the same amount this year. In 2014, cash flow was $354 million. This year it’s projected to rise to $370 million – still not enough to pay the distribution.

You’ll hear management talk about the fact that its cash flow does in fact cover the distribution – but that’s only to the limited partners and does not factor in the general partner. Unless the general partner stops receiving its distribution, you have to consider that cash flow is not covering the full distribution.

The company does have a very stable track record of paying the distribution, and cash flow is forecast to grow. But until I see cash flow covering both the limited and general partner’s distribution, NuStar cannot get my highest rating.