Before deregulation,
UA had Concourses E and F, except for 2 gates used by Ozark.
AA had K plus 2 gates on H.
After deregulation,
UA bulked up at
ORD, while
AA initially bulked up at
DFW. Eventually,
UA needed a new terminal, Terminal 1.
AA started buying up slots to compete with
UA. First,
AA took
DL's gate space on H, when
DL opened Concourse L. Then,
AA took Republic's gate space on H, after the merger with
NW.
It was after
AA had every gate on H and K that it did the significant renovation of these two concourses. To combat the growing traffic,
AA widened the aisle running down H and K, and removed many of the walls between all of the gates. This gave the concourses a more open feel, and didn't cut down tremendously on seating space in the gate areas.
Remember, H and K were originally built in the early 60s, so that the nose of an aircraft parked in a "slot" between two gates. These slots were "filled in", so that there is a glass curtain wall running the entire length of each concourse.
Then, in the late 80s and into the early 90s,
AA started taking
TW's space on G.
AA took complete control of G at the end of 1998, when
AC moved out of G-1. That led to the renovation that started in 1999.
AA started taking
DL gate space in the mid 90s. Frankly, I like Concourse L, because many of the gates are wide enough to handle widebodies. I think only L-1, L-2, and L-3 are narrowbody only.
If I recall correctly,
AA did a remodeling job of the gates in 1998 or 1999, about the time that the
MD-80s and 767s received new seats and interiors. The carpeting in the gates is the same color and pattern as on-board. That's also when the monitors went into every gate, so that agents didn't have to post flights, destinations, and times by hand.
AA has been deferring a lot of "cosmetic" work, such as painting jetbridges and the like, because of the finacial situation, as well as the fact that it can't grow at
ORD, most likely until the third east-west runway is finished.
The configuration of the "alleys" is a problem, particularly gates close to the terminal. To some degree,
AA doesn't have as great a problem, since the DC-10s are retired, and only a few 767s fly domestic routes. Thus, the widebodies pretty much park towards the end of K.
In that same vein, I don't think the gate spaces are that overcrowded. There
are far fewer widebodies going in and out of Terminal 3, compared to 15 years ago, and September 11th eliminated non-passengers on the concourses. Heck,
AA is in the process of removing all of the arrival monitors, except in the baggage claim.
From what I've heard, the terminal expansion plan is on indefinite hold. None of the airlines want to spend money right now. The configuration was supposed to be
UA and UAX domestic in T1,
UA international and Star airlines in
T2,
AA and Eagle domestic in
T3,
AA international and Oneworld airlines in
T4 (where the heating and a/c building is now), all other international carriers in
T5, and all domestic carriers that don't have space elsewhere plus new entrants in
T6.
However,
T2 and
T3 are having their ticketing areas and baggage claims renovated. The fronts of the terminals are being moved out 20 feet, new escalators are being installed, new lighting is going in, etc. The terminals are starting to look much better.