Some estimates say 100,000 barrels of crude are stolen from the Niger Delta every day, about 5 percent of daily output in the world's eighth biggest oil exporter, and equivalent to around $4 million a day at current prices.

Much of the oil is stolen by drilling into pipelines or hijacking barges laden with crude, theft known locally as "bunkering". The stolen cargo is then shipped out of Nigeria and sold on the international market.

The seven men were arrested by the military on Dec. 29 along the Chanomi creek, near Escravos in southern Delta state.

They pleaded not guilty to a two-count charge of conspiracy and illegally dealing in oil at a federal high court in southern Benin city, capital of the neighbouring state of Edo, the Economic and Financial Crimes Commission (EFCC) said.

Judge Mohammed Idris refused bail, ordered the accused be remanded in prison and adjourned the case to March 19.

A Nigerian court on Friday sentenced 13 Filipinos to five years each in prison or a $6,770 fine after they pleaded guilty to handling oil products suspected to have been stolen in the Niger Delta, the heart of Africa's biggest oil and gas industry.

The military impounded 22 barges of stolen crude about two weeks ago in what it said was its biggest seizure for months.