DENVER (CBS4) – Airline passengers at Denver International Airport say they aren’t surprised that four major airlines are being investigated by the Department of Justice for possibly working together to keep rates high.

Most DIA passengers said weren’t surprised given the current cost of flying and just about everyone CBS4 spoke with said they welcome an investigation.

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“It definitely hasn’t gone down,” a woman at DIA said.

“I have four kids. It costs so much more for all of us,” a man said. “It’s just outrageous. I’ve never seen anything like it.”

A traveler at DIA comments on the investigation (credit: CBS)

A traveler at DIA comments on the investigation (credit: CBS)

The average domestic airfare went up 13 percent between 2009 and 2014. Now the Department of Justice wants to know if four major airlines are working together to limit the number of seats and keep the airfares high.

CBS News found American, Southwest, United and Delta were all contacted as part of the federal investigation. For travelers in Denver the idea makes sense.

(credit: CBS)

(credit: CBS)

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“So we’ve got what, four or five major airlines? Even if it is an under-the-table sort of availability other than price fixing outright, the incentives are there, it just doesn’t surprise me,” the woman said.

For industry analyst Josh Marks it’s not as clear cut. He says airlines working with each other to limit capacity is unlikely.

“Technology today is so pervasive that airlines can watch what their competitors are doing in real time and make decisions almost instantly that change their level of capacity based on what somebody else is doing,” Marks said.

Whatever the investigation reveals, passengers say knowing someone is looking into it is reassuring.

A traveler at DIA comments on the investigation (credit: CBS)

A traveler at DIA comments on the investigation (credit: CBS)

“I’m just glad they are doing their job,” a traveler said.

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Several smaller airlines, including Jet Blue and Frontier, say they were not contacted by the Department of Justice.