In the absence of a formal coalition, May's government would survive from vote to vote in parliament - and with such a slim majority over the progressive parties, they would be vulnerable to defeats if there were absences or a threat to cross the floor.
Brexit Secretary David Davis said he would "fight tooth and nail" to keep Mrs May in post, and dismissed suggestions that he might be a contender to replace her.
There are 650 seats in the U.K.'s House of Commons, meaning that a party must win at least 326 seats to hold a majority and form a working government.
Among smaller parties, the pro-independence Scottish National Party is seeking to repeat its 2015 near-sweep of seats in Scotland.
Guenther Oettinger, a German member of the European Commission, said Friday that the election result had left it unclear whether negotiations between the United Kingdom and Europe on Britain's exit from the EU could be launched on June 19 as planned. In 1974, a minority Labour government was in charge for eight months because the Conservatives were willing to abstain on key votes. Given the election arithmetic, Labour would struggle to get the numbers to form a government.
The shock result and the prospect that the European Union will now be negotiating with a shaky British government cast dark clouds over the Brexit negotiations just 10 days before they are due to start. They're hardly going to make any major concessions, and she's going to have to go back to her Parliament with her divided party and try and get some obvious compromises through.
Cutting a deal with the DUP, which won 10 seats, may not be straightforward. The DUP - staunchly Eurosceptic, anti-abortion, anti-gay marriage - will demand a price for their cooperation; the kingmaker role has its advantages.
"I want the Conservative party to succeed, I want the Conservative party leader to succeed and I want us to be in government".
"May didn't have to call this election", said Pedley. Her predecessor, David Cameron, first asked British voters to decide in 2016 whether to leave the European Union or stay in, triggering the divorce that will leave the bloc with 27 members when Britain leaves in 2019.
"This suggests a less stable government, one that will have to make concessions and seek a consensus even when introducing simple changes to legislation", Schroders' senior European economist and strategist Azad Zangana says.
Tim Bale, professor of politics at Queen Mary University of London, said it's not even clear whether May will now lead those negotiations. Not only that, her authority was somewhat diminished by the fact that it took multiple recounts on Thursday night to confirm that she had retained her seat.
The recriminations were immediate and stinging. Cutting a deal with the DUP could enable May to remain in the Prime Minister's office, albeit with a far weaker mandate.
"Honestly, it feels nearly like she is nearly not aware of what has happened in the last 24 hours", Conservative lawmaker Heidi Allen told LBC radio.
If May stays in the longer term she will likely be forced to open up No 10 to a more consultative operation, having previously preferred to work with a tight-knit coterie of close advisers.