Originally Posted by flightexpert

Nope - it doesn't seem like there's any rhyme or reason to it. Code A will give 50% off while code B only gives 10%. But change the dates and location, and suddenly code B is better.

Also, some corporate codes give a whopping discount one time, then are practically useless on the next search. Same goes for the "up to 20% off" general use codes - sometimes 20%, sometimes 2%.