The Interactive Advertising Bureau has reported that U.S. online ad revenues reached $6.4 billion for the third quarter of 2010 – the highest quarterly result ever recorded.

The record number also represented a 17-percent growth since the third quarter of 2009, and it put the total revenues for 2010 at more than $18 billion. Assuming the year’s final quarter keeps pace, total revenues for 2010 will likely be around $25 billion.

Search continues to lead the industry with a 47-percent share of all online ad revenues, followed by display with 23 percent. Display’s third-quarter revenues climb to 34 percent if video and rich media advertising are included in the results.

The third-highest share of U.S. Internet ad revenues in the third quarter of 2010 belonged to classified and directory advertising, which accounted for 10 percent of the total.