The Grand Tour is the most effective of Amazon's original programming in terms of bringing first-time streamers to the service.
According to a report by Reuters, the first season of the show cost Amazon $49 (£38) per first stream.
Reuters said it has seen internal Amazon memos detailing the cost and viewership of nearly a number of Prime exclusive series. It says Amazon uses the "first-stream" information as a key indicator to determine a show's success.
According to Reuters, Amazon believes the first series a viewer chooses to watch after signing up deserves the credit for luring them to Prime.
The documents also reveal Amazon's top series drew more than five million viewers to sign up for Prime worldwide by early 2017 and Amazon’s US audience for all video programming on Prime, including films and TV shows it licenses from other companies, was "about 26 million customers."
Amazon has declined to comment on the report.