As their corpulent systems collide with increasingly harsh economic realities, airlines are making up more creative fees and charging for things that used to be free. Here's 9 of the worst offenders of the hidden airline fees, via Aviation.com.

9. Making a reservation on the phone or in person. Fee: $5-$20
8. Cashing in frequent flyer miles without "sufficient" advance notice. Fee: $0-100.
7. Bringing a pet onboard in the cabin/ Fee: $50-85 (each way)
6. Re-banking frequent flyer miles. Fee: $50-100
5. Checking luggage. Fee: $3-10 (each way)
4. Getting a refund when a fare goes down. Fee: $25 to $200 or more.
3. Flying standby on the same day of travel. Fee: $0-50
2. Paying for lap children. Fee: $10 to 10 percent of the adult fare
1. Getting a seat assignment. Fee: $5-$11 (each way)

What's your least favorite hidden airline fee?

Most Obnoxious Hidden Airline Fees [Aviation] (Thanks to Brandon!)