Originally Posted by rjque
Alaska does allow this but not on all fares. IIRC, Web Specials and some "IO" fares do not allow same day standby. Check the fare rules for your specific ticket or just call and ask.
Also watch out for fares with a "TR" (or "TS"?) in the code, which have time-restrictions. Standby is allowed, but only for flights within the permitted times. (Though if there are plenty of seats available the gate agents will often let you slide.)