The price cap, to be enforced by the G7, the European Union and Australia, comes on top of the EU's embargo on imports of Russian crude by sea and similar pledges by the United States, Canada, Japan and Britain.
It allows Russian oil to be shipped to third-party countries using G7 and EU tankers, insurance companies and credit institutions, only if the cargo is bought at or below the price cap.
Because the world's key shipping and insurance firms are based in G7 countries, the cap could make it difficult for Moscow to sell its oil for a higher price.
Russia, the world's second-largest oil exporter, said on Sunday it would not accept the cap and would not sell oil that is subject to it, even if it has to cut production.
In essence, such a decree would ban the export of oil and petroleum products to countries and companies that apply it.