Up until a few years ago, DL & NW have occupied the same terminal space and gates at PHL (Terminal E) since it opened in the mid-1970s.
CO & UA (minus the more recent Hammerhead D gates) have used the same gates at Terminal D for decades as well (again, PHL).
US has occupied most of if not all of Terminal B (& its gates) for decades also; dating back to when it was still AL (guess) and before PHL became a large hub for them.
EA occupied the original Terminal A (& its gates) from when it was built (60s) right up to the carrier's demise.
Until the new Terminal A came to be, I believe that at least some of the gates (maybe more?) that DL used in Terminal C date back to the 1972 merger w/NE and to when the terminal was first built (NE only).
[Edited 2010-06-22 10:41:01]
"TransEastern! You'll feel like you've never left the ground because we treat you like dirt!" SNL Parady ad circa 1981