The Nigerian state and oil -companies are losing $1bn or more a month to oil theft by criminal networks whose activities have expanded rapidly under the presidency of Goodluck Jonathan.

According to Ngozi Okonjo-Iweala, the finance minister, the trade in stolen oil led to a 17 per cent fall in official oil sales in April, or about 400,000 barrels per day. At average April prices of $121 per barrel, this implied a loss of $1.2bn. This is a higher estimate than that given by SPDC, Royal Dutch Shell’s -Nigerian subsidiary, which put theft at between 150,000b/d and 180,000b/d.

Ms Okonjo-Iweala said that the theft of oil – known in Nigeria as “bunkering” – along with fraud in the allocation of a -controversial fuel subsidy, might together have cost the state $14bn in 2011.