Opera Mediaworks said Android garnered 45.8% of total revenues generated on Opera's ad platform, compared to 45.4% for iOS during the period.
Opera reported that one year ago, Android had overtaken iOS as the top operating system for mobile ad traffic when measured by mobile ad impressions served. Android now has 65% of mobile ad impressions, while iOS has 22.3%.
Android ad traffic has grown at such a fast pace because of the rapid increase in the number of Android tablets and smartphones made by multiple manufacturers. With smartphones and feature phones alone, Android powers about 81% of the global market, compared to 15% for iOS, according to market research firm IDC.
Opera provides mobile ad services to 90% of the top global advertisers, which serve ads to 850 million mobile users on 18,000 sites and applications.
While Opera reported the percentage of ad revenues going to Android, the company would not divulge the actual dollars that it terms as mobile ad revenue.
According to eMarketer, mobile ad spending worldwide in 2015 will hit $68 billion and will mushroom to more than $100 billion in 2016. The overall dollars spent on mobile ads in 2014 surpassed $42 billion, eMarketer said.
IDC reported in March that spending for global mobile advertising will increase from $28 billion in 2014 to $39 billion in 2015 and $88 billion in 2018, according to an email from an IDC spokesman. IDC measures mobile search and display ads in its totals. It wasn't clear why eMarketer's numbers were so much higher.
Opera's use of the terminology "mobile ad revenue" includes what advertisers spent with Opera to use its mobile ad platform, as well as the revenues that the publishers of mobile Web sites and apps generated by using the Opera platform, according to Falguni Bhuta, vice president of communications for Opera Mediaworks.
Opera enabled about $1 billion in revenues for publishers last year, Bhuta said.
Other insights Opera revealed about mobile ads: