Internet advertising revenues jumped 40 percent in the first half of this year, driven largely by the growing popularity of keyword ads tied to search results.

U.S. revenues for the first six months were $4.6 billion, compared with $3.3 billion for the same period in 2003, according to a PricewaterhouseCoopers study conducted for the Interactive Advertising Bureau. Search made up 40 percent of the ad revenues in the second quarter of 2004, compared with 29 percent in the year-ago period.

Ad revenues from e-mail marketing dropped 29 percent in the second quarter to $47 million as many internet users equated legitimate pitches with spam. The figure includes ads within e-mail newsletters, e-mail marketing campaigns and other commercial e-mail communications from legitimate businesses.

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