United has...
--Ordered more large (70-seat) regional aircraft to replace smaller 50-seat RJs
--Reported to be considering a new 90-100 seat aircraft
--On order, more than 100 additional B737 aircraft
--Cancelled or delayed the retirements of many older 757 and 767 aircraft
--Converted orders of smaller B787 aircraft to larger B777 aircraft
--Received four used B737 aircraft from COPA
--Leased additional A319 aircraft from China with options for more
--Apparently over-scheduled their existing fleet this summer attempting to meet demand to the point that their schedule reliability is being affected
--Orders for the A350 aircraft
If they are involved in collusion to limit supply they aren't doing it very well...