I'll clarify my earlier answer.
I don't think you'll find that the airlines were dealing with this company. It's a physical oil trader. Other oil companies traded with it, not airlines. It deals (note the present tense) with oil and natural gas gathering, transport and storage. The biggest creditors are other oil firms, Husky in Canada is one.
SemGroup say they're going to flog off a lot of assets (which are worth over $6 billion). This is the important thing about Chapter 11, it allows companies time to reorganise whilst protected from creditors. As you'll know from airlines, Chapter 11 means that a (slimmed) phoenix can arise from the ashes.
with faceless suites of offices in a Texas skyscraper
Rainboe - Gotta head north a bit mate, they're based in Tulsa!
