Sigh.

s/Delta/United/ or s/Delta/Southwest/ or s/Delta/Lufthansa/. Or if you prefer, s/refinery/oilfield, or s/refinery/pipeline. Or even s/refinery/farm/ because Delta also buys food in vast quantities (I would not be surprised to find they have interests in ag producers that offset a small % of their food purchases, which does not diminish the argument).

Delta also does not make airplanes, jet engines, seats, radios, GPS, glass, or even wires. They don't distill the spirits they serve on their flights. They don't own and operate a satellite Internet capability. They don't even make movies for in-flight entertainment.

The point is that Delta, like most successful firms, outsources key aspects of core service delivery.

The second article you linked says plainly that the refinery is an offset/hedge. QED Delta still outsources the vast majority of its fuel costs. (They could, for example, own large swathes of the Permian and do E&P as well. They choose to leave that to others.)