Where do US ad buyers go for the best return on investment (ROI)? To Google and Facebook, naturally.

A December 2017 survey of US senior ad buyers by financial services firm Cowen and Company showed Google search was held in the highest esteem when it came to ROI. Nearly half of respondents named the platform as offering the highest ROI. Facebook ranked second, named by 30% of those polled.

Google and Facebook both improved their positions from last year. In 2016, the survey found that 32% of senior ad buyers thought Google search had the best ROI, while 27% chose Facebook.

In 2017, no other advertising platform garnered double-digit percentages among ad buyers. Just 8% of respondents thought ad exchanges and networks had the best ROI, while Instagram and YouTube were each named by just 4% of ad buyers.

Those responses align with the dominant position that Google and Facebook are widely perceived to hold among the digital advertising landscape—both in the US and globally.

eMarketer estimates Google and Facebook combined will account for more than 65% of US digital ad revenues in 2018.

Google alone is expected to capture $40.08 billion in net ad revenues in the US this year, while Facebook is projected to bring in $21.57 billion.

"Advertisers are increasingly demanding more granularity in targeting capabilities to reach consumers. Google and Facebook have positioned themselves at the front of this demand curve by being the ad publishers with some of the best-in-class targeting abilities in the digital ad market," said Monica Peart, eMarketer's senior director of forecasting.