Microsoft, which also offers flight and hotel search with Bing Travel, fought Google's acquisition of I.T.A.
Google's flight search joins other travel offerings, like hotel search, which it introduced in July.
Other travel Web sites have been enhancing their own hotel search features.
Mobissimo, which made its debut in March, began offering a hotel search feature this month.
For a hotel search in New York City you could, say, set the outline to show hotels below 14th Street.
BookDifferent.com, a hotel search engine that donates part of its commission to charity has started listing environmentally friendly hotels.
Explore is bundled with Kayak's online suite, which includes flight and hotel search options, and a useful list of airline fees.
Hipmunk.com Similarly focused on finding a good deal in a good location, Hipmunk's hotel search, which made its debut in March, is best for Web-savvy travelers.
Google.com/Hotelfinder Google's experimental hotel search site, which started in July, focuses on where to stay and finding a good deal.
It has not yet introduced flight search tools and the company said the hotel search did not use I.T.A.'s technology.
In October, it said it had purchased Kuxun.cn, a Chinese flight and hotel search engine, as part of plans to invest $50 million in China through 2011.
