A lot of historical data is used in determining how and when to increase prices. You may see a price increase but if consumers do not book tickets and the seats do not get filled then CO will lower the prices again the following day to stimulate demand or for their fares to be competitive.

Also with the spike in gas prices, more leisure travellers are using the airlines for summer travel. If X # of seats are sold in a particular fare class that fare class is closed and the next higher fare class becomes avaliable.