The 13 members of the Organization of Petroleum Exporting Countries (OPEC) pumped an average 31.87 million barrels per day (b/d) of crude oil in April, a 350,000 b/d decrease from March, according to a Platts survey of OPEC and oil industry officials released Friday. The sharp drop was largely the result of steep output losses in Nigeria.

Excluding Iraq, the 12 members which participate in output agreements pumped an average 29.49 million b/d, 360,000 b/d down from an estimated 29.85 million b/d in March.

"OPEC production has been relatively steady in recent months, but the sharp fall in Nigerian output shows how vulnerable overall supply from the group can be to developments in one country," said John Kingston, Platts global director of oil. "Given that spare capacity is also relatively tight, any disruption has a bigger impact on markets."

Ongoing losses in Nigerian supply as a result of continuing strife in the Niger Delta were exacerbated by a week-long pay strike at ExxonMobil, which shut down most of the company's 800,000 b/d of production and forced it to declare force majeure on exports from the 400,000 b/d Qua Iboe terminal.

Other smaller decreases came from Angola, Iran, Qatar, Saudi Arabia and Venezuela. Iraqi volumes were a shade higher at 2.38 million b/d, with a slight dip in exports offset by slightly higher internal supply. Libyan output also edged up, to 1.75 million b/d from 1.74 million b/d in March. The latest estimates show the OPEC-12 missing their 29.673 million b/d output target by 183,000 b/d.