By Cassie Werber

LONDON--The amount of crude oil due to be pumped from fields in the North Sea is set to fall nearly 15% in May compared to the previous month, as maintenance season takes large swathes of production out of the market.

The Oseberg field will load only two cargoes this month, according to provisional loading programs seen by The Wall Street Journal, compared with six last month.

"I think it's just normal field maintenance [and] I would say it was planned. Whether or not the market knew about it until very recently is another matter," said Steve Sawyer, an oil consultant at FACTS Global Energy.

The total number of barrels to be loaded in May will be 24 million, down 14.9% from 28.2 million the month before.

A North Sea oil trader said that the "large maintenance" was likely priced in, and that the Oseberg field is undergoing maintenance between the April 25 and May 15.

The loadings of the other three grades that make up the BFOE basket of crudes used to create the Brent benchmark were similar to the previous month.

Loading programs are released and circulated among oil traders and brokers, but don't give a perfect indication of oil volume because they can be subject to change.

Brent crude is of international importance because it remains one of the most liquid markets and influences oil prices across the globe.

North Sea loading programs:

                  April 2014                   May 2014 
 
               (barrels)    Volume (B/D) (barrels)    Volume (B/D) 
Brent          3,600,000    120,000      3,600,000    116,129 
Forties       11,400,000    380,000     10,200,000    329,032 
Oseberg        3,000,000    100,000      1,200,000     38,710 
Ekofisk       10,200,000    340,000      9,000,000    290,323 
Total BFOE    28,200,000    940,000     24,000,000    774,194 
 

Write to Cassie Werber at cassie.werber@wsj.com