Carriers availability: Soft-sided carriers that are 3 1/2 pounds empty are available for $60 (nonrefundable).

Special restrictions: No cargo pets.

Perks: TrueBlue travelers with pets earn double JetBlue miles.

NORTHWEST

Pets in cabin: Dogs, cats and household birds.

Pets as checked baggage: Allowed. Dogs, cats, household birds and other pets such as rabbits and hamsters can travel with your luggage on domestic flights; advance arrangements are required, and the airline recommends you choose nonstop flights. Only dogs and cats can travel with luggage on international flights.

Cost: $80 each way in the cabin. For pets traveling with luggage, the cost is from $139 for small pets to $359 for animals weighing 150 pounds or more.

How many: One per traveler.

Maximum pets per flight: Six carry-on pets per flight.

Booking your pet: For carry-on pets, call Northwest reservations and pay fees in advance. For checked pets, check the website before calling, www.nwa.com, or call (800) 225-2525.

Carrier restrictions: Combined weight of carry-on kennel and pet not more than 15 pounds. Carriers must be leak-proof and ventilated on two sides.

Carrier availability: None.

Restrictions: Because of heat, embargo from June 1 through Sept. 15 for pets traveling to Las Vegas and all cities in Alabama, Arizona, Arkansas, Florida, Louisiana, Mississippi and Texas.

Perks: Offers the Priority Pet Program, with employee training at all locations and transportation in heated and pressurized luggage compartments. Also offers a more costly same-day shipping service for pets traveling in cargo.

SOUTHWEST

Pets: No pets allowed.

UNITED AIRLINES

Pets in cabin: Dogs, cats and household birds.

Pets as checked baggage: Cats, dogs and household birds. For other animals, contact United Cargo at www.unitedcargo.com

Cost: Cabin pets cost $85 each way; in cargo, it's $100 for smaller pets and $200 for medium-size to extra-large pets.