David Cameron has said there is a “a pathway to a deal” on new terms for Britain’s membership of the EU after talks with other leaders.
The prime minister set out his reform demands, which include controversial plans to curb access to benefits for migrants, at a dinner in Brussels.
He said “good progress” has been made but it would be “hard work” to get a deal by his February deadline.
German Chancellor Angela Merkel said the leaders “all want a compromise”.
Mr Cameron wants to get a new deal before putting the question of the UK’s membership of the EU to an in-out referendum of British people by the end of 2017.
He is demanding change on four issues, including stopping in-work benefits for EU migrants in the UK for four years.
BBC political correspondent Alex Forsyth said she understood a number of ideas were “kicked around the dinner table” by the EU’s 28 heads of state on Thursday night.
There was suggestion among them that a legally binding agreement – and potentially treaty change down the line – would be possible, she said.
However, officials only had a very short time frame in which to hammer out the technical details by February, she added.
Official conclusions published by the European Council said members had agreed “to work closely together to find mutually satisfactory solutions in all the four areas”.