Several OPEC members, led by Saudi Arabia and Libya, put enough new barrels on the market in September to offset a drop in production from Iran, where U.S. sanctions are whittling away at the nation’s crude exports, according to a monthly report.

The 15-nation producer group also knocked down its forecast for oil demand in 2018 and 2019, and said the outlook for economic growth is softening, particularly in emerging markets. Meanwhile, OPEC raised its forecast for oil supply growth in 2018 from non-member nations, including the United States

The report comes just three weeks before a U.S. deadline for oil buyers to cut off imports from Iran, OPEC’s third biggest producer. Concerns about OPEC’s ability to fill the gap in crude supplies has pushed oil prices to nearly four-year highs above $86 a barrel, according to CNBC.

In September, OPEC pumped nearly 32.8 million barrels per day, up 132,000 bpd from August, according to figures supplied by several independent sources and cited by the group in its monthly report.

OPEC now expects world oil demand to grow by 1.54 million bpd this year, down 80,000 bpd from its last forecast. Meanwhile, it raised its outlook for supply growth from non-OPEC countries by 200,000 bpd to 2.22 million bpd.