Must be leak-proof and allow the dog to stand up and turn around. Soft-sided carriers are best for fitting under seats.

Some boutique or luxury airlines, such as JSX , allow you to purchase an actual adjacent seat for a larger dog to sit on the floor in front of.

Proof of rabies vaccination is the standard minimum for domestic travel.

A unique option for medium-to-large dogs; allows you to buy a full-priced second seat for your dog to travel in the cabin with you. Traveling with pets - United Airlines

Fee is $150 per kennel for in-cabin travel. Requires check-in at the ticket counter with a health certificate.

Charges a flat $150 fee each way for in-cabin pets. You can easily add this during the checkout process on their website.

You can often add a pet via the "My Trips" section of an airline's website or app.