NEW YORK, Aug. 1 (Xinhua) -- Oil prices suffered big losses Monday, with the U.S. oil hitting below 40 U.S. dollars a barrel for the first time since April, as a survey showed that output in the Organization of the Petroleum Exporting Countries (OPEC) reached record highs last month.

Production in July by the OPEC likely rose to its highest level in recent history, as Iraq pumped more and Nigeria squeezed out additional crude exports despite militant attacks on oil installations, according to a Reuters survey Friday.

Meanwhile, the number of rigs operating in U.S. fields added by 44 in July, the most in a month since April 2014, data from oil services company Baker Hughes showed.

Demand for crude is also set to fall in the next few months. U.S. refineries usually reduce operating rates to perform seasonal maintenance as the summer driving season comes to an end.

The West Texas Intermediate for September delivery dropped 1.54 dollars to settle at 40.06 dollars a barrel on the New York Mercantile Exchange, while Brent crude for October delivery plunged 1.39 dollars to close at 42.14 dollars a barrel on the London ICE Futures Exchange.