Online advertising revenue in the US breached a significant barrier in the year's third quarter, notching $3.1 billion (€2.64bn; £1.8bn) within the period.
Internet ad sales rose 34% over the same period in 2004, according to the Interactive Advertising Bureau and auditor PricewaterhouseCoopers.
The IAB forecasts that online ad revenue for 2005 could top $12bn, well above last year's total of $9.6bn.
Says PWC's David Silverman: "Clearly advertisers are realizing the benefits of shifting more of their total advertising budgets to online."
But despite the relentless hype, online ads still account only for a small proportion of the total US ad market which reached $71bn in the first half of this year, according to researcher TNS Media Intelligence.
Data sourced from Wall Street Journal Online and latimes.com; additional content by WARC staff