Ministers from the Organization of the Petroleum Exporting Countries (OPEC) are gathering meet in Vienna on June 14 to discuss whether to cut oil production.
Oil prices have dropped below $100 from a recent high of about $130 in March.
Analysts say the price drop is due in part to extra production from Saudi Arabia.
Riyadh has been pumping more crude in part to make up for a drop in sales of Iranian oil due to U.S. sanctions over Iran's refusal to curb its nuclear program.
World oil supplies could be squeezed further when a European Union embargo on Iranian crude takes effect on July 1.
Iran has warned Saudi Arabia not to ship more oil to countries that no longer get Iranian crude due to sanctions.
The Saudi oil minister has said his country sells to whoever buys.
Based on reporting by AP and Reuters