President Muhammadu Buhari is to visit the Gulf for a week-long tour, with a focus on ending the global slump in oil prices that has hammered Nigeria's crude-reliant economy, his office said on Sunday. Buhari, accompanied by Emmanuel Ibe Kachikwu, the junior oil minister and head of the state-run oil firm, begins his trip in Riyadh on Monday, meeting King Salman bin Abdulaziz and senior Saudi officials. "Ongoing efforts by Nigeria and other members of the Organisation of Petroleum Exporting Countries (OPEC) to achieve greater stability in the price of oil exports are expected to be high on the agenda of discussions between President Buhari and the Saudi monarch," a statement read.