"A contract with Rosneft company has been prepared which is large-scale and unprecedented without any exaggeration," Putin told Chinese Vice Premier Zhang Gaoli at a meeting in Saint Petersburg, estimating the value of the deal at more than USD 60 billion.
In his comments open to the media, Putin did not say when the firm contract would be signed.
A preliminary agreement to gradually raise Russian oil supplies to China over the next 25 years from their current level of 15 million tonnes per year was reached during China's leader Xi Jinping's visit to Moscow in March.
Russia, which wants to diversify its energy customers away from Europe, also needs to finalise a potentially huge gas deal with China but a commercial contract has so far proved elusive as talks have become mired in pricing disputes.