'97 mis-firing when accellerating

My 97 with 31K miles started to mis-fire about a 2weeks ago. It's only noticable when I accellerate from a dead stop, and it seems to be getting worse (longer duration). It started out as about 2-5 seconds of rough running, and now it lasts a good 10-15 seconds, then clears out. Once at cruising speed, engine runs smooth, and also idles smooth. No SES light, so I wonder if it may be bad gas?
Ideas? Thanks.
Mike

Have you tryed changing your fuel filter? if not that.. id say plugs and wires.. have had the same problem with mine, but havent gotten around to dropping down the $100 for the wires..