EMarketer forecast online ad spending next year to reach $7.8 billion based on a continued surge in search engine marketing.
However, "the dark side of paid search emerges from its 'hypergrowth,'" said David Hallerman, senior analyst at eMarketer.
He said budgets for paid search take away money that would have been allocated for other forms of online advertising, including rich media.
Search accounted for $1.6 billion in ad spending this year; that number is expected to increase to $2.1 billion next year and $4.3 billion by 2008.
EMarketer benchmarks its spending figures and projections against Interactive Advertising Bureau/PricewaterhouseCoopers data.