What’s going on here?

Most of the well-known online travel agencies are owned by just two companies Expedia (Expedia, Orbitz, Travelocity, Hotels.com, Hotwire) and Booking Holdings, formerly Priceline Group (Agoda, Booking.com, Kayak, Priceline).

Checkbook believes this lack of competition hurts consumers. Expedia and Booking Holdings disagree. They say they are simply online marketers who display prices set by the hotels.

Representatives from both companies told NBC News BETTER that many hotel chains require parity agreements that prohibit them from undercutting the rate set by the hotel.

“We don’t set the prices, they set the prices,” said Leslie Cafferty, senior vice president of communications at Booking Holdings. “But the agreement is that they’ll list the same price wherever they list it. So, if they list the room at $100 a night on their website, then they will list it at $100 on our website.”

Dave McNamee, Expedia’s director of communications, offered a similar sentiment. “The value we offer our customers is matching travelers with the best hotel for their needs at the best price available for us to offer,” McNamee said in a statement.

Expedia suggested Checkbook found minimal price variation because they only looked at the base rates set by the hotels and did not log-in to take advantage of the deals offered to members.

“It is incredibly easy for travelers to save up to 10 percent or more on over 175,000 participating hotels just by simply signing up and logging in to Expedia.com,” McNamee told NBC News BETTER.

Checkbook’s Brasler told us they did not include these membership discounts in their analysis, but they did check what each site offered as “unlockable” rates — not otherwise available when searching the internet.

“We found sometimes these rates knocked off up to 10 percent from the prevailing rate. So, not exactly a game changer, but it’s worth checking for these discounts before clicking buy,” he said.

Expedia noted that bundling — booking a flight and hotel at the same time — can result in significant savings. A new option, Add-On Advantage, allows travelers to qualify for hotel discounts of up to 43 percent at any point before their trip, if they book a flight, car or package on Expedia.com, the company said.