Finance ministers of the 16 states which use the euro agreed by video conference on Sunday the final details of a financial safety net to save Greece from the risk of default.
"Eurogroup members have agreed on the terms and operational modalities of coordinated financial support to be swiftly activated if needed," said the EU's commissioner for the euro, Olli Rehn, dpa reported.
Luxembourg Prime Minister Jean-Claude Juncker, who chaired the meeting, said the loan would be 30 billion euros (40.5 billion dollars) in first year.
He said this would be combined money from the European Union and the International Monetary Fund (IMF), but stressed Greece had not yet asked for any aid.
Rehn said interest on the loan would be around 5 per cent.
Greece's finances have been under massive pressure on the money markets in recent months, raising the fear that it will no longer be able to borrow enough to service its debts.
The euro has tumbled and the value of Greek government bonds has plummeted in recent days as investors raised doubts over the credibility of a safety net agreed by European Union leaders at a summit in Brussels on March 25.
The urgent talks, called Saturday, were the third eurozone attempt to shore up market confidence in Greece's ability to pay its debts.
In February, an EU summit pledged to maintain the stability of the whole eurozone, of which Greece is a member. Markets remained unimpressed, charging Athens a risk premium of over 6 per cent on government bonds, double the rate charged to bellwether Germany.
A further EU summit in late March provided more details, confirming that the EU and International Monetary Fund would offer Greece a bail-out if it found it unable to borrow on the markets.
Investors welcomed that announcement, but their enthusiasm cooled this week as Greek officials reportedly questioned the desirability of involving the IMF, and EU leaders refused to state how much they would pay and what interest they would charge for any bail-out.