Unlike most of the other fees, airlines are introducing additional charges that some people are more than happy to pay. For some extra money, fliers can enjoy a more comfortable flight.

Some of the upgrades start off with basic extra legroom and even quiet lounge areas, but it also extends to electronics. Apple iPads are even available to rent, with full movies already downloaded. However, some airlines have taken to using technology to target certain fliers.

The airport itself offers a great opportunity to test out such technology. For example, some airlines can go so far as to track individual fliers within an airport. They aim to make it so that if someone clears security too early, that individual might be offered a discounted day pass for the airport.

“We have massive amounts of data,” Delta CEO Richard Anderson says through registerguard.com. “We know who you are. We know what your history has been on the airline.”

However, many people find fault in being tracked throughout the airport, believing it to be an invasion of privacy. Because of these justified fears, most airlines have kept to using their data to find fliers whose flights have been delayed.

While airlines want their customers to be comfortable before, during, and after the flight, the main reason for these optional fees is the rise in jet fuel prices. The fact remains that most fares simply can’t cover the expenses of flying. When airlines attempted to raise ticket prices, people went to different websites to find lower fares or, even worse for airlines, didn’t travel at all. In 2008, oil prices spiked, causing most airlines to raise the cost of checked-baggage.

Now, customers can use these optional fees to fly more comfortably. For instance, an empty seat can be arranged for a small fee, or fliers in coach can purchase meals normally served in first class.

These options also make life easier once customers reach their destination. Anyone can pay for their baggage to be delivered. Not only can passengers skip the hassle of the baggage carousel, but it is also faster, making it easier to stay on time if the flight was delayed.

Bundled packages also offer extra income for airlines. Delta offers a package which charges passengers for a subscription that included a checked bag, early boarding and access to exit row seats.

United Airlines has customized their own fees based on demand. Due to the extra legroom of aisle seats, these seats now cost more than the middle seats.

Southwest, meanwhile, offers an upgrade for passengers selected to board last that allows them to bypass the line and jump to the front. While neither of these price changes are huge hits, it helps bring in revenue without adding extra expenses.