2003 was particularly painful, as the A's were up 2-0... they lost Game 3 on an 11th inning walkoff. Lost Game 4 after leading 4-2 in the 8th. Lost Game 5 after leading 1-0 in the 7th.
So the A's are 1-11 in their last 12 playoff series. Seven of those losses have come in Game 5.