Revenues for digital advertising in the U.S. reached a historical US$27.5 billion in the first semester of 2015, according to an IAB report. The figure marks a 19% increase over the US$23.1 billion in ad revenues for the first semester of 2014. The growth was particularly big in the second quarter of 2015 when ad revenues rose by 22.5% reaching US$14.3 billion.The report also revealed that advertisers invest more in mobile advertising. The segment presented a 54% investment increase in the first half of the year, with US$8.200 million. Mobile advertising represents 30% of the revenues generated by the entire internet advertising marketplace, up from 23% in the first semester of 2014.Advertising on social networks increased 51% during the first semester of this year, reaching US$4.400 million.