Reports from Cannes say the world's biggest economies will agree to increase the International Monetary Fund's resources by allowing countries to make voluntary contributions.
"States that wish to, can, from around the autumn of 2012, raise their bilateral participation in IMF resources," said a source quoted by the AFP news agency. Leaders of the G20 countries are holding two days of talks in the French town.
The fund's resources were boosted by a deal a year ago doubling the contributions of IMF permanent member states.
That agreement was meant to take effect a year from now but several national parliaments have yet to ratify it, so in the meantime member states had made temporary resources available to the IMF through lending agreements.
But under the new deal, those temporary arrangements would now become permanent if the member countries chose to make them so, the source said.
Participants in the G20 talks said they also discussed constructing a financial firewall to protect vulnerable euro zone economies Italy and Spain from a possible Greek default.
The leaders of China, Russia and the United States pressed the Europeans to move more swiftly to contain the debt crisis, with Washington urging Germany to relent and let the ECB play a greater role in financial firefighting, G20 sources said.
Canadian Prime Minister Stephen Harper said the leaders had discussed contingency plans if Greece were to leave the euro zone, "but my expectation is that cooler heads will prevail and the package will be accepted (by Greece)".
