NEW YORK: Internet ad revenues in the US reached a record high of $27.5bn in the first half of 2015, according to new figures from the Interactive Advertising Bureau (IAB).

The IAB Internet Advertising Revenue Report, prepared by PwC US, revealed a 19% rise over the same period in 2014, the biggest first-half increase since 2011.

Data are compiled directly from information supplied by companies selling advertisements on the internet and include figures for online advertising revenues from web sites, commercial online services, free email providers, and all other companies selling online advertising.

Search continues to be the single biggest ad format, accounting for 37% of spending and growing 11% to break the $10bn barrier for the first time.

Mobile, meanwhile, has overtaken desktop display to claim second place; mobile revenues surged 54% to $8.2bn in the first half, and it now takes 30% of digital adspend compared to 23% a year ago.

Desktop display's share slipped back from 28% to 25% over the same period and spending edged up 5% to $6.8bn.

Within the display category, however, digital video has grown strongly, up 35% to almost $2bn. Spending on all other display formats – banners, sponsorships and rich media – declined.

In terms of platform, social media continues its onward march: spending on social networking sites, social gaming websites and apps leapt 51% to $4.4bn.

"We're witnessing a seismic shift in consumer behaviour to the always-on, connected consumer," said David Silverman, a partner at PwC US. "As a result, we've seen social continue to fuel the growth of digital, particularly with respect to mobile and video."

Randall Rothenberg, President and CEO, IAB, noted that advertisers were more committed than ever to connecting with these consumers. "Content is key to winning consumer attention – on mobile, in digital video, on desktop, and more – throughout the day," he said.

The top three advertising verticals were unchanged with retail (22%), financial services (13%), and automotive (13%) accounting for almost half of all advertising revenues.

Data sourced from IAB; additional content by Warc staff