Internet advertising revenues in the United States jumped 22 percent in 2011 to a record $31 billion, amid sizzling growth in the fledgling mobile Web space, industry figures showed Wednesday. The 2011 figures were up sharply from 2010 -- already a record level of $26 billion -- following a first-ever decline in 2009, the Internet Advertising Bureau said in a report prepared by consultants PwC. \"This historic moment, with an especially impressive achievement in mobile, is indicative of an increased awareness from advertisers that they need to reach consumers where they are spending their time -- in digital media,\" said Randall Rothenberg, IAB president and chief executive. \"Pushing past the $30 billion barrier, the interactive advertising industry confirms its central place in media. Across search, display, digital video, digital provides a wealth of opportunity for brands and consumers,\" Rothenberg said. \"With the proliferation of smartphones and tablets, it is likely that the tremendous growth in mobile will continue as these screens become even more crucial to the marketing mix.\" Fourth quarter ad revenues for 2011 hit a best-ever at $9 billion, and were up 15 percent increase over the third quarter 2011. Mobile experienced the fastest growth of all categories, up 149 percent to $1.6 billion in 2011 from $600 million in 2010. \"The year 2011 saw mobile advertising become a meaningful category,\" said David Silverman, of PwC. \"By combining some of the best features of the Internet, along with portability and location-based technology, mobile advertising is enabling marketers to deliver timely, targeted, relevant, and local advertisements in a manner that was not previously possible. It is for these reasons that we expect strong growth to continue with mobile advertising.\" Digital video ads, a component of display-related advertising, saw a 29 percent increase year-over-year to $1.8 billion. Search revenues accounted for the biggest share in 2011, $14.8 billion, up almost 27 percent for the year. Another big category, Internet display ads, accounted for $11.1 billion in revenue, an increase of 35 percent. Retail advertisers continue to represent the largest category of Internet ad spending, accounting for 22 percent in 2011, or $7.1 billion, compared with 21 percent in 2010, the report showed.