Nigeria is a major oil producer but most of this is sent abroad while it has to import the refined fuel used in vehicles and elsewhere.
As a result the country often faces chronic fuel shortages.
This is the problem that the $19bn (£15.2bn) refinery, owned by Africa’s richest man, Aliko Dangote, is intended to tackle.
“This is a game-changer for the Nigerian people,” said President Muhammadu Buhari.
The plant, which is not yet operational, has the capacity to produce about 650,000 barrels of petroleum products a day – more than enough to supply the country’s needs. It also includes a power station, deep seaport and fertiliser plant.
Nigeria’s existing refineries have been completely shut down for over three years owing to oil theft, pipeline vandalism and structural neglect.
At Monday’s launch, Mr Dangote outlined his hopes for the refinery: “Our first goal is to ramp up production of the various products to ensure that within this year, we are able to fully satisfy the nation’s demand for quality products.”
However, it is not clear what impact the plant will have on the price of fuel in a country where retail prices are subsidised. The government says these subsidies will soon be removed – last year they took up nearly a third of the national budget.
It is also not clear how the refinery will get its oil as there is no pipeline connecting it to Nigeria’s oil fields: “I’m assuming they’d use ships and barges to supply crude to the refinery,” oil and gas expert Henry Adigun told the BBC.
Mr Dangote’s plant in Lagos, which took nearly seven years to build, is said to be the world’s largest single-train refinery, meaning the plant has one integrated distillery system which can produce a variety of products and petrochemicals, instead of having different units for each type of product.
It is one of the last major projects to be inaugurated by President Buhari, who steps down next week after serving two terms in office.
He will hand power to Bola Tinubu, who won disputed presidential elections in February.
Mr Adigun said Monday’s launch was “more political than technical”.
