Washington ? Plenty of vacation guides list camps that allow dogs or rank pet-friendly hotels, but until now there has been no way to know which airlines are safest for four-legged travelers.

That’s about to change. Starting June 15, airlines must report how many pets are killed, lost or injured on their flights.

The government estimates 2 million animals fly commercially every year. Many airlines allow small pets to travel in portable kennels under seats, where the owners are responsible for their safety. Larger pets travel in cargo holds, where they can be exposed to extreme heat or cold and loud noises from plane engines.

Nobody knows how many pets are killed or injured. Lisa Weisberg, spokeswoman for the American Society for the Prevention of Cruelty to Animals, suggested 1 percent, which would mean 20,000 animals per year. The airlines say that’s far too high.

But no one disputes that accidents do happen.

When Sarah Stano’s husband was transferred from Portland, Ore., to Greensboro, N.C., she chose Delta Airlines to fly them there because it was the only airline that would let her carry her three cats in the cabin.

But at the airport she discovered one of the containers was too big to fit under the seat. Hereford, a fluffy white cat with black spots, had to go in the cargo hold.

Graphic shows tips on flying your pet; two sizes; 1c x 7 inches; 46.5 mm x 178mm; 3c x 3 1/4 inches; 96.3 mm x 83 mm; ETA 3 p.m.

“I’ll never forget the look he gave me when they took him away,” Stano said.

When Stano and her two children arrived late at night in Greensboro, they found out Hereford had died from either cold or lack of cabin pressure. “We were really kind of devastated about the whole thing,” Stano said.

Stano sued Delta and reached an undisclosed settlement.

Delta spokeswoman Benet Wilson said the airline didn’t comment on individual cases.

Weisberg’s organization pushed Congress to pass the law requiring the airlines to report animal casualties. Supporters wanted it to cover animals shipped to zoos and those used for research and breeding, as well as household pets, and to require that cargo holds be temperature-controlled.

Airlines fought the effort, and lawmakers ended up approving a rule that requires tallying injuries and deaths of household pets.

Jack Evans, spokesman for the Air Transport Assn., said the requirement could produce misleading information because the data would not include a casualty rate. An airline that carries many pets may appear to have a worse record than an airline that carries far fewer animals because it will have a higher number of injuries and deaths, said Evans, whose organization represents major airlines.

David Stempler, president of the Airline Travelers Assn., said the new requirement might make some airlines reluctant to carry animals.

“Be careful what you wish for,” Stempler said. “Some carriers might do what Southwest does, which is not carry pets at all.”

Southwest spokeswoman Edna Ruano said the airline couldn’t guarantee that animals would be comfortable and safe because it didn’t have extra staff to take care of them between flights. Like most airlines, Southwest does allow seeing-eye dogs and other service animals in the cabin.

United Air Lines transports all types of animals, and has awarded extra frequent flier miles to people who bring their pets with them.