“Hotel companies are not going to give every channel the same price now — parity deals — that were written into the conditions of the agreement” in the past, Ms. Woodley added. There can be five different prices for the same room, she said. “So for consumers, it’s a better environment.”

The days of the rapid growth of the online travel agencies are gone. “Online travel in the U.S. is mature,” said Henry Harteveldt, a travel industry analyst at Hudson Crossing. “Growth is flattening out. There isn’t double-digit growth like in the late 1990s and early 2000s,” he said. “Online travel agencies are exploring new ways to reach more people — acquisition and investments. Kayak and Trivago will refer more business to the respective purchasers.”

In March, Expedia ranked second after TripAdvisor, with Priceline third among the top 10 online travel agencies and search sites, for the “number of unique visitors,” according to comScore, which tracks visitors to travel and other types of Web sites. In March, TripAdvisor had nearly 20.95 million visitors, followed closely by Expedia with 20.92 million, and Priceline had 17.45 million. Kayak.com Network ranked eighth with 8.94 million visitors, with Trivago Sites ranking 248th with 142,000. Online travel agencies make money through online advertising more than through transactions, Mr. Harteveldt said.

While many analysts said they expected online travel search to remain much the same after the acquisitions, one argued that the parent company could now favor its own companies in its search results of hotels, for instance, or when it sells advertising. Kayak is “not neutral anymore,” said Edward M. Woo, senior research analyst of digital media for Ascendiant Capital Markets.

“They’re owned by Priceline now,” he said. “It will be hard to keep the barriers between them and Priceline. Within a year, how impartial is Kayak able to be when Priceline is Kayak’s biggest customer? Expedia won’t want to advertise on Kayak. Kayak doesn’t care if it loses Expedia ads. They got the money.” Priceline paid $1.8 billion for Kayak, including $500 million in cash and $1.3 billion in equity and assumed stock options, according to Priceline.

Mr. Woo predicted the rise of another search engine “that will be neutral.”

In March, the British Office of Fair Trading said it would review the Priceline-Kayak deal. The office accused Priceline’s hotel reservation site, Booking.com, and Expedia of breaking both European and British competition laws by signing deals in July with InterContinental Hotels Group that limited discounts on hotel rooms.

Mr. Woo said he expected that regulators would approve the Priceline-Kayak deal. “Antitrust can go after them later on, but once the deal is through, there is no way to regulate the future,” he said. A decision is expected in early May.