Countries that have made voluntary cuts that exceed those agreed with the broader group are Algeria, Iraq, Kazakhstan, Kuwait, Oman, Russia, Saudi Arabia and the United Arab Emirates.
The group will have a series of online and in-person meetings on Sunday, starting with an OPEC ministers-only meeting at around 0930 GMT.
OPEC+ sources said several key ministers – mainly from countries that have made voluntary cuts – arrived in the Saudi capital Riyadh. Other ministers will join online.