Global proved oil reserves were 1732 billion barrels at the end of 2020, down 2 billion barrels versus 2019. OPEC holds 70.2% of global reserves. The top countries in terms of reserves are Venezuela (17.5% of global reserves), closely followed by Saudi Arabia (17.2%) and Canada (9.7%).
Details at BP here
Source: BP - Statistical Review of World Energy 2021 Report