An oil leak found in a shared pipeline in Nigeria has forced oil companies to shut down their daily production of 180,000 barrels of crude oil.

Royal Dutch Shell PLC, which owns 30 percent of the Sambarth-Karkrama pipeline, has not yet discovered the cause of the leak, located in the eastern part of the Niger Delta.

The pipeline was shut down over the weekend after the problem was discovered on Friday. Authorities are trying to determine the cause, but residents in the region were preventing them from arriving on site to investigate, a Shell spokesman said Tuesday.

Shell and its partners experienced have experienced a total loss of 653,000 barrel per day in production.

Oil companies in Nigeria have experienced various oil production difficulties recently.

Shell, the Anglo-Dutch giant, normally pumps more than half of 2.5 million barrels of oil in Nigeria each day. However it has suffered several attacks by armed militants this year.

ChevronTexaco said the leak was costing it 30,000 barrels per day in production losses.

On Tuesday, light sweet crude futures for September delivery traded at $73.65 a barrel, down $1.40 on the New York Mercantile Exchange.