Both Yahoo! and Microsoft (MSFT) are actively pitching Apple to take over the coveted contract, according to news outlet TheInformation. And Yahoo! chief executive Marissa Mayer candidly admitted to shareholders that she really wants the deal. "The Safari platform is basically one of the premiere search engines in the world, if not the premiere search engine in the world. We are definitely in the search distribution business ... and anyone who is in that business needs to be interested in the Safari deal," Mayer said during Yahoo!'s December quarter earnings conference call with investors. "The Safari users are among the most engaged and lucrative users in the world and it's something that we would really like to be able to provide." At stake is the prized Safari audience on Apple iPhones and iPads, an audience that in the U.S. accounts for 69% of all tablet users and 50% of all mobile users, Cullen said. Also ripe for the taking are mobile search advertising dollars, which will top desktop search ads for the first time this year. Research firm eMarketer estimates that U.S. search ad spending on mobile will total nearly $13 billion in 2015, up from $9 billion in 2014. In contrast, spending on desktop search ads is expected to fall to $12.3 billion in 2015, down from roughly $13.6 billion in 2014. "Google really does get the lion's share of mobile search referrals," Cathy Boyle, eMarketer senior mobile analyst, said. "If they were to lose that relationship with Apple, and no longer be the engine behind Safari, they stand to lose a significant portion of that share." Google doesn't break out mobile revenue, but executives emphasized the positive impact of mobile search during the company's fourth quarter earnings call. Google reported adjusted earnings of $6.88 per share, weaker than the expected $7.11 a share on revenue of $18.1 billion for the quarter. "We continued to see great traction with our established mobile advertising products," Google Interim Chief Business Officer Omid Kordestani told analysts, highlighting mobile advertising revenue from YouTube, which grew 100% year-over-year. "We are very pleased with the traction we are having and how mobile monetization is performing."