Frontier Airlines allows small pets to travel in-cabin or as checked pets. In-cabin pets must fit in a carrier under the seat and cost $99 each way. There is a limit to the number of in-cabin pets per flight. Checked pets are transported in the cargo hold, with fees ranging from approximately $150 to $250 each way, depending on size and weight. Advance booking and compliance with Frontier's guidelines are necessary for checked pets. It's important to check Frontier's official website or contact their customer service for the most up-to-date information on their pet policy and fees.