The FIA has the option to change the format of qualifying to reflect the 18-car entry that it is expected in Austin next weekend, with both Caterham and Marussia failing to make the trip.
Currently six cars are eliminated in both Q1 and Q2. With an 18-car field that would mean that only two cars would be bumped out in Q1 – and with Sebastian Vettel having already stated that he will sit out qualifying due to a power unit change guaranteeing a pitlane start, in reality we could see only one car bumped in Austin.
However, the FIA Sporting Regulations include the provision for changing the number of cars that are eliminated. The numbers specifically referred to are eight for a 26-car entry, and seven for a 24 car entry. It follows that with an 18-car entry four cars would be bumped from Q1 and Q2.
The regulations refer to the size of the ‘championship’ entry rather than that for an individual race. However sources confirm that once the stewards have officially been notified that only 18 cars are in the Austin field they will have the option to decree that four cars are eliminated in Q1 and Q2.
Adam Cooper's F1 Blog 
Thanks AC, it’s amazing for F-1 wanting to put on the big show in Amerika but seems to fall flat at getting another track here or enough cars on the only track here. Sad, greed will kill f-1.
Should do 5 and 5… leave only 8 in the shootout… The pole shootout the positions 6-10 get ignored anyway!
….. and the track owners in Austin are already making noises about not making enough money due to having to PAY THE LITTLE TROLL’S EXORBITANT FEE! (sorry for shouting). Is there no one who has any common sense involved in running the sport?