More agencies and their parent companies are stepping up online investments in what is known as search marketing or search engine marketing, an estimated $5.1 billion category last year that has been growing far faster than traditional advertising in media like television and newspapers.

The goal of the agencies and agency companies is to offer search marketing services internally rather than requiring clients to go to independent specialist agencies.

At first, marketers "burned at the beginning of the decade by the dot-com bust" hesitated to spend ad dollars on search marketing, said David Hallerman, senior analyst at eMarketer, a research company in New York.

Now, "they have seen it is very effective," he added, and are expanding their spending into nascent realms like video search. Last week, eMarketer forecast that ad revenue from search engine marketing would climb to almost $6.5 billion this year, from $5.1 billion in 2005, and reach more than $10 billion by 2009.

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