The Associated Press reported that airlines in the U.S. made more than $6 billion in baggage and reservation change fees in 2012.

"Airlines started charging for a first checked suitcase in 2008 and the fees have climbed since. Airlines typically charge $25 each way for the first checked bag, $35 for the second bag and then various extra amounts for overweight or oversized bags," reported The AP.

Delta Airlines collected $7.44 per passenger which was about average, while Spirit Airlines collected the most, at an average $19.99 per passenger for baggage fees.

The airlines made $159.5 billion in revenue in 2012 and had expenses of $153.6 billion, reported the government to the AP. The profit margin is from baggage and change fees. Delta Air Lines took in the most fees with $865.9 million from baggage alone, but it also had the most passengers.

To change flight reservations, it's not a cheap cost. A number of airlines including Delta, United Airlines and American all raised their flight reservation change fees for domestic flights from $150 to $200.

"Airfares have climbed in recent years but jet fuel remains costly - in 2012, the airlines paid an average of $2.96 a gallon. Passengers have shown reluctance to book tickets if the base fare is too high, hence the introduction of more fees - collectively referred to in the industry as ancillary revenue," reported The AP. But the airlines are being aggressive about expanding those fees. United recently said in an internal newsletter that it hopes to collect $19.29 in average ancillary revenue per passenger by the end of 2013, up 9.1 percent from the amount it collected last year."

JetBlue is one airline that doesn't charge for the first checked bag but it still took in $22 per passenger in other fees in the first quarter.