United Airlines has the following policies on pet-travel:
Pets are allowed as both carry-on and checked luggage.
Fees: $125 each way as carry-on, and $250 each way when traveling as checked baggage.
– Passengers are required to make sure all health and pet travel documents are current and compliant with local, state, federal and international entry requirements and regulations.
– Dogs, cats, rabbits, and household birds are allowed as carry-on.
– Some other pets, including dogs of the pit bull breed, hamsters and guinea pigs, may travel as checked baggage only.
For complete guidelines, check their site at: United Airlines