For many pet lovers, a vacation wouldn't be complete without their dog or cat beside them.

But taking a pet on a plane can be tricky. Negotiating the maze of travel restrictions, which vary widely from airline to airline, is daunting. Many carriers allow small dogs or cats to ride under the seat in front of you; others don't. Some will take a large dog in the cargo hold in a kennel. Other airlines won't allow pets, period.

It's especially important to check the rules if you're traveling in the summer or winter, when many airlines have restrictions because of extreme temperatures. In the summer, some airlines prohibit pet travel to cities where the temperatures are really hot, such as Las Vegas. Sitting on the tarmac in a kennel when it's boiling hot can kill a pet.

Here's a rundown of some of the major airlines and their current policies. This information applies only to pets, not to certified service animals, such as seeing-eye dogs, because airlines are required to follow government regulations on travel for such animals.

Once you select an airline, remember to check the rules on vaccinations and a pet's health status, which can differ from state to state. International guidelines are even more complex.

ALASKA AIRLINES

Pets in cabin: Dogs, cats, rabbits and household birds.

Pets as luggage: Alaska and Horizon Air accept most small domesticated pets in the climate-controlled luggage compartment. Other pets may be accepted with approval. Pets accepted include dogs, cats, ferrets, hamsters, guinea pigs, pot-bellied pigs and nonpoisonous reptiles.

Cost: $75 each way in the cabin. In cargo, it's $100 each way for a pet and kennel weighing up to 149 pounds combined.

Limit: One per traveler.

How many pets per flight: In the cabin, one in first class and five in the main cabin, for a total of six per flight.

Booking your pet: Call (800) 252-7522 in advance.

Carrier restrictions: In the cabin, the carrier must fit under the seat, and the pet must be able to move comfortably. Dimensions vary. See the website, or call reservations for specifics. In the climate-controlled luggage compartment, the largest kennel Alaska will accept is what is known as a 500-size.

Carrier availability: A limited number of in-cabin carriers are for sale at most airport locations. Please arrange in advance.

Special restrictions: If the temperature is too hot or too cold, the airline may not take pets in the cargo hold. Animals with offensive odors or those that are noisy must travel in the hold.

Perks: Once a pet is loaded into the luggage compartment, a ticket confirming the animal is onboard is delivered to the traveler.

AMERICAN AIRLINES

Pets in cabin: Cats and dogs only, 20-pound limit.

Pets checked as luggage: Two pets and two kennels are allowed per passenger, with each pet in a kennel; there are some exceptions (contact the airline). The maximum weight with a kennel is 100 pounds.