The search engine war over Safari is heating up. Google has long served as the default search engine on the Apple web browser, but with that arrangement reportedly set to expire in early 2015, Yahoo and Microsoft are jockeying for the role.

There’s a lot of power in the default setting. Since Yahoo started powering search on Firefox by default, the company’s been steadily (albeit slowly) eating away at Google’s lead, which in January dropped below 75% of US search share—the first time it’s fallen below that level since at least 2008, according to visitor-tracking firm StatCounter.

When the firm removed Firefox searches from its calculations, however, Yahoo’s gains and Google’s losses all but disappeared. “The numbers showed conclusively that the default search setting could have a big effect on what search engine gets used,” StatCounter CEO Aodhan Cullen tells Quartz.

It’s especially big stakes when it comes to Safari, which in January accounted for 48% of searches on smartphones, 69% on tablets, and 9% on desktops in the US, according to Statcounter. It’s still anybody’s game at this point, but here are the possible scenarios to consider:

Yahoo wins

CEO Marissa Mayer’s been eyeing search on Apple’s mobile devices for a while now—and mobile is one of her main priorities for turning around the company. “The Safari platform is basically one of the premier search deals in the world—if not the premier search deal in the world,” she said in a recent earnings call with investors. “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.”

IDC research director Dave Schubmehl considers Yahoo search “a very worthy competitor,” citing the company’s investment in research and development, but not everyone thinks such a scenario is plausible. Collin Colburn, senior research associate at Forrester Research, said that while Yahoo has made gains in its search product, “usability is still not as good as Google.”

Bing wins

Microsoft already powers web searches on Apple’s personal assistant application, Siri, as well as the Spotlight search tool on Macs running the newest desktop operating system, Yosemite. Why wouldn’t its search tool, Bing, have a shot at Safari? “It seems logical since the search capabilities of Bing has improved tremendously over the last couple years,” says Schubmehl.

Microsoft appears committed to making Bing ubiquitous. “All the places where people go today, we want to be,” Stefan Weitz, director of search for Bing, said last fall, citing integrations with iOS, Twitter, Facebook, and Amazon as examples. If Apple intends to chip away at Google’s dominance, the company might choose to put its weight behind Bing, which is currently Google’s biggest rival in search. But as this could turn to a bidding war, it’ll also depend on how much Microsoft wants this deal.

Apple sticks with Google

Apple is a company that’s staked its reputation on great user experience. And Google, the dominant search engine by far, has been continually tweaking its algorithm to get answers to users faster. This can be seen with the contextual information (stock quotes, weather forecasts, sport scores) that now shows up in answer boxes stacked above search results.

However, not all the innovation is viewed favorably. Apple might hesitate to renew its partnership with Google given the threat to Siri from voice search and Google Now, which presents users with relevant and timely information. The two companies, of course, also have their fundamental differences when it comes to consumer privacy and data collection, which leads us to a fourth option…

Apple decides to go at it alone

Perhaps the most interesting scenario of all is the one in which Apple builds its own search engine. “If they were to dump Google, I think it’d be in favor of their own search engine because it’s been talked about in the past two to three years,” says Colburn. As with Apple Maps, it would be the ultimate way to control the user experience.

Apple already began diverting user queries away from Google with its Spotlight search on Yosemite. It may be no coincidence, then, that the company earlier this week posted a job listing for an engineering project manager overseeing something called “Apple Search,” which according to the description will be ”a search platform supporting hundreds of millions of users.”