When you are a master limited partnership as sound as Enterprise Products Partners (NYSE:EPD), any problem you might experience from quarter-to-quarter, or year-to-year, can really stand out -- even in the face of solid earnings.

A quick look at the partnership's third quarter gross operating margin does just that. Here's how Enterprise's margins look on a segment-by-segment basis compared to last year's results:

Source: Enterprise Products Partners

Every segment is up on an annual basis, or at least relatively flat, except for the petrochemical and refined products unit. Sticking out like a sore thumb, this segment suffered a $65 million drop off from last year's number. There are several businesses that comprise this segment, so let's take a closer look at exactly what drove this loss.

The bulk of the damage came at the hands of the propylene business, where gross margin was basically cut in half from $55 million to $28 million. Fractionation and pipeline volumes in petrochemical were up slightly compared to 2012, but it wasn't enough to fend off the decline in sales margins and the rise in operating costs, which included a plant turnaround.

This segment was also dinged by a $26 million decrease in the marine transportation unit, but only because last year the segment received a $24 million boost from a legal settlement. All of which reminds us that sometimes year-over-year comparisons, fun as they are to make, do not always properly indicate the health of an operating segment.

The only real takeaway from a tough quarter for the petrochemicals and refined products segment is that commodity prices hurt, and will continue to hurt until prices rise.

Now, if Enterprise's sole business was its petrochemical and refined products segment, investors would be pretty distraught. It's not, clearly, and there was a lot to like coming out of the partnership this quarter, including record volumes for the following segments:

  • NGL transportation
  • Crude oil transportation
  • NGL fractionation
  • LPG exports

Not only is the partnership extremely diverse in its operations, which mitigates tough quarters in the segments exposed to commodity risk, but it derives a significant amount of its revenue from fee-based agreements. That means when volumes reach historical highs, as they did this past quarter, the money flows.

These record volumes contributed directly to a gross operating margin increase of $100 million year over year. Expansion efforts coming to fruition, given Eagle Ford, Seaway pipeline, and propane loading, were the driving factors behind the growth.

All told, it was a strong quarter for Enterprise Products Partners, a company that finds a way to win regardless of the price environment for commodities.