LONDON (Reuters) - OPEC oil supply in April is expected to slip by 100,000 barrels per day (bpd) from March, led by lower supply from Iraq, Iran and Nigeria, an industry consultant said on Friday.

All 13 members of the Organization of the Petroleum Exporting Countries are set to pump 32.5 million bpd this month compared with a revised 32.6 million bpd in March, Conrad Gerber of tanker tracker Petrologistics, told Reuters.

Accounting for the slight decline, the exporter group continued to pump significantly more than its supply limit during a month when oil sped to a record high near $120 a barrel. "There is not much change," Gerber told Reuters. "Much of the decline comes from Iraq being down, although there are some increases here and there."

The April estimate suggests the 12 OPEC members bound by deals to set production policy, all except Iraq, are pumping 30.24 million bpd -- well above their informal target of 29.67 million bpd.

Iraq is producing 2.26 million bpd in April, down from 2.35 million bpd in March, due to slower exports.

Output from Iran, OPEC's second-biggest producer, is down 50,000 bpd in April at 4.15 million bpd.

Nigerian supply is 100,000 bpd lower in April at 1.95 million bpd due to militant attacks.

April production from top world exporter Saudi Arabia is steady at 9.15 million bpd.

Pumping higher are the UAE, with output of 2.55 million bpd versus 2.49 million bpd in March and Algeria, with production at 1.38 million bpd in April, versus 1.32 million bpd in March.