It's spring break time, and plenty of people are planning trips — and renting cars.

And that brings many questions: Do you want to prepay your fuel? What are all those mysterious fees? Should you pay for extra insurance?

To address prepaying for fuel, TODAY national investigative Jeff Rossen and two members of the Rossen Reports team rented the same make and model car (a 2016 Toyota Camry SE) from the same place before driving to the Grand Canyon, but paid three different ways. Jovanna Billington prepaid at the counter; Rossen did not prepay, and filled the tank just before returning the car at the end of the trip; and Josh Davis didn't prepay and didn't fill up the car before returning.

After they all drove the same distance — two hours to the Grand Canyon and two hours back — Davis paid the most for gas: $59.22. Billington was charged $41.65 for the entire tank, even though she used only about half. The money-saving winner was Rossen: $16.74. "So the moral of the story is, unless you're going to drip that tank empty, fill it up yourself," Rossen said.

Travel expert Gary Leff explained the many fees you may see on your rental charge:

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Concession recovery fee: "The rental company has to pay the airport to rent you a car, so they are going to charge you for that fee," Leff said.

Tire and battery recovery fee: "Tires wear out; they are going to have to be replaced," Leff explained. "You pay them to throw away old tires."

Customer transportation fee: That "free" shuttle that takes you to and from the airport "isn't so free, and you pay whether you use it or not," Leff said.

Parking recovery fee: "When you are not renting the car and they are not renting it to someone else, it's got to park somewhere, and they are charging you for the parking."

Energy recovery fee: To offset the significant costs of utility charges, bus fuel, oil and grease, and related costs.

Air conditioner surcharge: The company that makes the car pays a tax on the air conditioner installed in it; that gets passed on to the rental company, which passes it on to you.

City-based fees: All vehicle rental transactions in Boston are subject to a $10 surcharge to help pay for convention centers in Massachusetts. Cleveland requires car rental companies to collect a Motor Vehicle Lessor Tax to finance various city projects. And Kansas City imposes a daily $6 fee to provide funds to a downtown area.

How can you avoid such fees? "Most of the fees stem from renting at the airport," Gary Leff said. You can avoid them by taking a taxi or Uber to a downtown car lot to rent your car there. "You can even return it to the airport, because it is leaving the airport with a rental car that triggers the fee."

And what about that insurance they try to get you to buy at the counter:Do you really need it? Leff's advice: Before you rent the car, check your own car insurance. Many policies already cover collision for rental cars.

If yours doesn't, also check the credit card you use: Some cards cover your insurance, too. (Liabilty may not be covered, but you should check.)

To suggest a topic for an upcoming investigation, visit the Rossen Reports Facebook page.