Before a my last trip on continental in late February on one 1,700 mile segment F availability went from F7 to F2 6 days before departure, by the next morning I had not gotten an EUA and it was F0! By noon it as back up to F5!!! During all this time it was a constant A9, meaning that not more then 5 out of 14 seats on the 738 were booked. I called the OnePass Service Center to complain about manipulation of inventory for FC upgrades. They connected me with a reservations supervisor who did the upgrade. The flight actually left with one empty seat in first!.