NEW YORK: Google's share of mobile advertising expenditure in the US is set to dip below 50% in 2013 before recovering over the next two years, according to latest estimates from eMarketer.

The insights company forecast that Google would account for 48.2% of net US mobile internet ad revenues in 2013, compared to 52.5% in 2012. This figure was expected to creep back up to 50.6% by 2015.

In addition, eMarketer estimated that in 2013, some 19.1% of Google's US ad revenues would come from mobile search, up from 12.3% last year and rising to nearly 31% by 2015. Similarly, mobile display will account for 3.8% of US ad revenues this year, rising to 9.4% by 2015.

Google's only significant competitor is Facebook, which has come from nothing – it did not offer mobile ads in 2011 – to take a 9.4% share in 2012 and a predicted 15.3% in 2013. It is expected to maintain that share into 2014 before slipping back to 13.1% in 2015.

The shares of other named firms, including YP, Pandora, Twitter and Apple, hovered around 3% to 4% and were not expected to change significantly. And eMarketer expected "other" firms to take a combined one in five mobile US ad dollars for the foreseeable future.

When considering overall digital ad revenues – including desktops and laptops as well as mobile – Google continued to dominate, with a 41.1% share anticipated for 2013, forecast to increase to 44.0% by 2015.

Google's nearest rival is currently Yahoo!, with a 7.7% share forecast for 2103, closely followed by Facebook on 7.1%. But by 2014 these positions and shares will be reversed.

Facebook will continue to strengthen in 2015, by when it will account for 8.3% of net US digital ad revenues.

These three companies were followed by Microsoft on around 5%, IAC and AOL on around 2.5%, and Amazon and Twitter on around 2%.

Data sourced from eMarketer; additional content by Warc staff