2009 financial crisis, but the harmony has now gone.
There are likely to be some agreements - including on measures to fight tax evasion by multinational companies - at the summit in the spectacular, 18th-century Peterhof palace complex, built on the orders of Tsar Peter the Great.
An initiative will be presented to leaders on refining regulation of the $630-trillion global market for financial derivatives to prevent a possible markets blow-up.
Steps to give the so-called 'shadow banking' sector until 2015 to comply with new global rules will also be discussed.
But consensus is proving hard to achieve among developed economies as the United States takes aggressive action to spur demand and Europe moves more slowly to let go of austerity.
The emerging economies in the BRICS group - Brazil, Russia, India, China and South Africa - urged the G20 to boost global demand and ensure that any changes in monetary policy are well flagged to minimise any disruptive "spillovers" that may result.
The appeal reflected the concerns among developing nations over the prospect that the Fed will scale back its ultra-loose monetary policy, and a view that Europe is not doing enough to promote a demand-driven recovery.
The BRICS also agreed to contribute $100 billion to a joint currency reserve pool. China will commit $41 billion; Brazil, India and Russia $18 billion each; and South Africa $5 billion.
Russia and China also joined forces in warning about the potential impact of the Fed ending its bond-buying programme to stimulate the economy.