ALEXANDRIA, Virginia, Sept 10 (Reuters) -

News Corp ( NWSA ) in 2017 estimated losing at least $9 billion in ad

revenue that year if it had switched away from Google's massive

advertising apparatus, keeping the media conglomerate captive to

the Big Tech company, a former News Corp executive testified on

Tuesday.

"I felt like they were holding us hostage," Stephanie

Layser said the second day of Google's antitrust trial in

Virginia.

Google frustrated publishers by introducing features

that benefited itself more than them, said Layser, who worked in

advertising technology at News Corp ( NWSA ) from 2017 to 2022. However,

almost no one in the industry used anything else, because

Google's publisher ad server is tied to Google's ad exchange,

she said.

The trial is expected to last several weeks, with the U.S.

Department of Justice seeking to show that Google monopolized

markets for publisher ad servers, advertiser ad networks and the

ad exchanges that connect the two.

NewsCorp documents shown at trial estimated that in 2016,

the publisher made $83.3 million from ads sold instantaneously

through ad tech tools. More than half of those transactions went

through Google's ad exchange, with $18.4 million from Google ads

advertisers.

The publisher estimated that around half of that, or $9

million, was exclusive to Google and would be lost in any shift

to another product.

By the time she left, around 70-80% of News Corp ( NWSA ) ad

transactions flowed through Google's ad exchange, Layser said.

Google has said that the case is based on an outdated look

at the industry, and that large publishers use an average of six

different platforms to sell ads that there are more than 80 such

services.

At trial, prosecutors are seeking to show Google used

dominant positions in technology for publishers and advertisers

to keep them from using other tools and undercut bids placed

through competitors' products.

Layser was the second publisher witness to testify at

the trial. Tim Wolfe, an advertising executive at Gannett ( GCI )

, testified on Monday that the company has used Google's

publisher ad server for around 13 years, and that there are no

other realistic options.

Google adtech competitors such as Trade Desk ( TTD ),

Comcast ( CMCSA ) and PubMatic ( PUBM ) are on the list of

potential witnesses, as are more than two dozen current or

former Google employees and executives.

If U.S. District Judge Leonie Brinkema finds that Google

broke the law, she would consider prosecutors' request to make

Google at least sell off Google Ad Manager, a platform that

includes the company's publisher ad server and its ad exchange.