In the UK, the study estimates advertisers spend £112m ($152m) on misinformation sites, while in Europe the figure is €407m (£349m, $475m).
Major brands, including Pepsi, Starbucks, Verizon and Marriott have had their ads placed on misinformation sites. Comcast, which owns reputable media companies such as NBC and Sky, has also had ads placed on misinformation sites.
Although the figures sound large, the study found the problem only applied to about 1.68% of display ad spend among the sample of 7,500 sites.
In the US, the analysis showed that for every $2.16 in digital ad revenue sent to legitimate newsbrands, US advertisers send $1 to misinformation websites.
Since the pandemic began, websites that peddle Covid-19 myths have become a major brand safety issue.
NewsGuard, which has been tracking the issue, recently found more than 4,000 brands, including Covid vaccine maker Pfizer, health insurers and the US Centers for Disease Control and Prevention, had unintentionally bought ads that fund misinformation websites that promote Covid-19 conspiracy theories and misinformation.
NewsGuard partners agencies within IPG, Publicis Groupe and Omnicom. It also works with demand side platforms MediaMath, Amobee, Verizon DSP, Centro, Xandr and supply side platforms GumGum, TripleLift, Teads and IndexExchange.
It provides a service where journalists curate credible website inclusion lists for advertisers.
NewsGuard UK managing director Alex Cadier said a recent case study found that when an advertiser targets ads to credible sites, their average CPM reduces by 9% and click-through rates increase by 143%.