eMarketer updated its forecast for ad spending purchased through real-time bidding, which will make up 19% of total digital display ad spend in the US in 2013. The previous forecast, out in November 2012, was increased slightly and the company added its 2017 forecast.

According to eMarketer, US RTB digital display ad spending, for all display formats served to all devices, will reach nearly $3.4 billion in 2013, a 73% increase over 2012. This will grow to $4.6 billion in 2014, a 36% increase, and by 2017, ad spending in the US RTB market will be $8.5 billion, or 29% of total digital display ad spending.

"The major change there is that there is no major change," Clark Fredricksen, an eMarketer spokesperson and researcher, told AdExchanger. "We increased the numbers slightly because of faster-than-expected growth and multiple sources showing adoption rates a little higher than they thought they would be at this point." He also highlighted the influence of Facebook Exchange, noting that "interest in the Facebook Exchange has been tremendous, so we expect that to contribute to growth as well."

The research firm also reported that there are challenges to RTB spending, including the complex eco-system, concerns about cannibalization from publishers, and concerns about transparency from buyers. But, as Fredricksen noted, Facebook and other major publishers have the chance to lead the way by increasing RTB inventory and boosting interest and spending in the market.