The refinery, funded at a cost of $20 billion by Africa's richest man, Aliko Dangote, is being built at Lekki, on the outskirts of the commercial capital Lagos.

Nigeria currently imports most of its fuel but the Dangote refinery will make it self sufficient and able to export fuel to neighbours in West Africa, potentially transforming oil trading in the Atlantic Basin as Nigeria challenges U.S. and European energy companies that for years have powered the cars, trucks and generators in Africa.

The plant received 1 million barrels of oil from the Agbami field in the Niger Delta, bringing to 6 million barrels the amount of crude that has been delivered since the first cargo arrived in December, Dangote's spokesperson said in a statement.

The next step is to start up the crude distillation unit, which is a major component of the refinery, a senior company executive, who spoke on condition of anonymity, said. That process would "most probably" begin this week, the executive added.

"Subsequently, we will be continuously buying crude and start commissioning the other departments," said the executive.

"Saleable products will start coming from the first week itself. But, of course, the volume will be limited and the variety of saleable products will also be limited and it will start building up, as each major department gets commissioned."

Experts say test runs include the different units that make products from gasoline to diesel and making sure they respond to the control panels. It can take months for refineries to move from test runs to producing high-quality fuels at full capacity, according to the experts.

Dangote has said it will start by refining 350,000 bpd and hopes to ramp up to full production later this year.

(Reporting by MacDonald Dzirutwe; Editing by Susan Fenton)