Curious About Airline "Collusion"

Why do most major airlines raise or decrease fares altogether? If one airline raise prices usually they all follow and if they don't then the airline that first increased prices rolls them back. Is there collusion within the airline industry? - Brad, Peabody

In fact United and Continental raised their prices late last week.  And while that may seem suspicious, it seems to be just the way the marketplace works.  In order for it to be collusion at least 2 of the companies must agree ahead of time to raise their prices.  And it doesn't look like that's happening.  It seems to be more of a competitive thing.

However it has happened before.  In the early 90's the government sued 8 major airlines for using a computerized system that allowed the airlines to agree on ticket price hikes before they were announced to the public.

Will you be flying this summer?  How expensive is it?