Yahoo Mail accounted for 4 of 10 online display ad impressions in August, blowing away competitors.

Yahoo Mail's 41.4 percent share of all display ads was more that three times that of closest competitor MySpace's 16.1 percent, writes MediaPost, citing Nielsen/NetRatings AdRelevance data. MSN Hotmail was third, with 7.8 percent of display ads. Yahoo's share increased significantly from the previous month's 32.9 percent and the 7.6 percent in August 2005.

Financial services companies accounted for 28.0 percent of online display ads in August, followed by retail goods and services with 18 percent and web media with 14 percent.

The total number of CPM display ads tracked by Nielsen (not pre-roll, partnerships and sponsorships) totaled 233.5 billion, up from 187.2 in July, 193.6 billion in June, and 197.7 billion in May.