But on the witness stand, Sundar Pichai, Google’s chief executive, said there was “value” in being the default search engine on a device and framed the agreements with other companies as sound business decisions.

Google paid $26.3 billion for its search engine to be the default selection on mobile and desktop browsers in 2021, according to the company’s internal data presented during the trial. Most of that, around $18 billion, went to Apple, The New York Times has reported. Kevin Murphy, a Google economic expert, testified on Monday that Google shared 36 percent of search revenue from the default deal with Apple.

Mr. Pichai testified that he repeatedly renewed the search engine deal with Apple because it worked well, leading to an increase in search usage and revenue and benefiting Apple, Google and its shareholders. He said Google paid Apple so much to protect users’ search experience on iPhones, not knowing if Apple would degrade that experience if Google hadn’t improved the financial terms of the deal.

“There was a lot of uncertainty about what would happen if the deal didn’t exist,” he said.

Google is not the only search game in town

To rebuff the idea that other search engines were too small to compete for default status on browsers, Google’s lawyers argued at the trial that rivals had been able to win contracts but could not hold on to them because of the poor quality of their products.

They cited an instance in 2014 when Mozilla, which makes the Firefox browser, exited a default-search partnership with Google and selected Yahoo.