Pilot program connects Google AdWords links and in-store sales.
Six advertisers are participating in a new Google test which will reveal the impact of web advertising on in-store behaviour.
"We are running a number of tests to help clients use their own sales data to measure how their search campaigns impact sales," said a Google spokesman.
Google pay-per-click advertising pays Google - and, where higher visitor volumes are involved, the website(s) hosting the ad - when users click on an ad and visit the advertiser's website. Google is the world-leader in pay-per-click marketing.
Its rival, Facebook, has already empirically demonstrated the effectiveness of advertising on its site by accessing data on in-store sales.
Both internet giants use specialist data companies to compile names, emails and addresses of millions of consumers, along with in-store purchase histories. Although these companies share their data with one another, consumers' identities are anonymised through the use of an algorithm which scrambles the data into random numbers.