One of the most popular places to start planning a vacation online is at an Internet search engine such as Google or Yahoo. But consumers need to understand what they are seeing and using.

Type "Las Vegas" in the Google search box, and you get a list of websites about traveling to Las Vegas. The top result (after maps of Las Vegas) may be, an online travel agency that specializes in Sin City. Also near the top of the results are sites about Las Vegas that are not trying to sell anything.

There are clearly marked "sponsored links" at the top of the page from travel agencies and others that are trying to sell Vegas vacations, but the results beneath are driven by Google's algorithm that determines the best match for a search term based on popularity and other factors.

On Yahoo, the search results page was altered in April. Type "Las Vegas" into the Yahoo search box and between the sponsored results at the top of the page and the actual search results (which are otherwise similar to Google's) is a link to "Las Vegas NV Visitors Guide." Click it and it takes you to Yahoo Travel. Change your search slightly to "Las Vegas flights" and a Yahoo box comes to the top of the search results. It's dubbed "Farechase," and it allows shoppers to search for flights to Las Vegas from the search results page.

Yahoo has inserted at the top of the search results page its own, proprietary travel offerings. "It's just a logical step [for Yahoo] to exploit the Farechase asset, now having it pop up more often," said Lorraine Sileo, an industry analyst for Connecticut-based PhoCusWright, a travel research firm.

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