Nigeria is Africa's biggest oil producer. But the fall in crude oil prices has Nigerians preparing for a below average economy this year.Nigeria's economy has long been linked to oil. The country now produces more than two million barrels of oil a day.Experts are worried, however, because crude oil prices have fallen below $30 a barrel. In 2014, oil was still valued at over $100 a barrel.Nearly 70 percent of the Nigerian government's revenue comes from the sale of oil. Oil makes up over two-thirds of Nigeria's exports.That puts the country in a difficult position, according to energy experts."Oil is basically government's main source of revenue of running the economy, or running the budget," said Dolapo Oni, Ecobank's Head of Energy Research.When elected in 2015, President Muhammadu Buhari promised to provide jobs and to stop corruption. Those promises led to a 25 percent proposed budget increase over the year before.