New detail on just how much Google is willing to pay to be a go-to search engine has slipped out in court in the US, where the tech giant is on trial defending itself from monopoly claims.

An expert testifying on behalf of Google said it sends 36% of the advertising revenue it makes on Apple's Safari web browser to the iPhone maker.

The relationship between the two firms is at the heart of the monopoly case.

Prosecutors say their dealings have illegally restricted competition.

The lead lawyer for Google "visibly cringed" when the specific share of ad revenue sent to Apple was revealed, according to Bloomberg.

Google has maintained that its dominance of online searches is due to having a superior product.

The high-stakes trial pitting Google against the US Department of Justice started in September. Many of the proceedings have been shielded from public view, to protect trade secrets.

But some details have emerged.

All told, Google paid more than $26bn to other companies, including Apple, Samsung and Mozilla, be installed as the default search engine, according to statements heard at the trial.

Analysts on Wall Street have estimated that amounted to more than $18bn for Apple alone.

University of Chicago professor Kevin Murphy, who revealed the share of advertising revenue Google sends to Apple from traffic on Safari, was testifying that the hefty sums Google and parent company Alphabet pay are evidence of the stiff competition in the market – one of the arguments advanced by Google.

The trial is expected to wrap up in the coming days, after a parade of witnesses, who have included Alphabet chief Sundar Pichai and Microsoft boss Satya Nadella.

Prosecutors from the US Department of Justice are seeking stiff penalties, including an end to anti-competitive practices.

A ruling against Google could have major implications for the tech industry, even if it falls short of a break-up of the company.

Judge Amit Mehta, who has been overseeing the proceedings, is not expected to rule on the case until early next year.