• by Steve McClellan  @mp_mcclellan, April 29, 2013

ZenithOptimedia revised its 2013 global ad spending forecast Monday, predicting that expenditures will climb 3.9% to $518 billion. That’s down slightly from the 4.1% gain it initially forecast last December for the year.  The shop reiterated that spending would pick up a bit in the following two years climbing 5% and 5.6% in 2014 and 2015 respectively.

For the U.S., ZO left its ad spending forecast unchanged for this year, reiterating that it expects a gain of 3.5% for the year to a little more than $166 billion. The U.S. will also see modestly higher growth in the following two years, ZO predicted, forecasting a gain of 4.3% in 2014 and a 4.8% gain in 2015.

Internet will continue to drive most the growth, ZO said, predicting that the medium will post a 14% gain worldwide, compared to just a 1.6% increase for traditional media in 2013.