It appears Nigeria may never be free from stories of theft and official corruption.

The excess money from crude oil sales which Nigeria saves for the rainy day is among the most mismanaged funds in the world.

This is according to a report by the Natural Resource Governance Institute (NRGI) released on Wednesday.

The $2.4 billion account was ranked alongside the Qatar Investment Authority as the worst in terms of oversight and transparency in NRGI's index of resource management.

NRGI rated 11 sovereign wealth funds, managing at least $1.5 trillion in total, as "failing".

According to the report, "The government discloses almost none of the rules or practices governing deposits, withdrawals or investments of the Excess Crude Account."

The report added that the account, along with the other worst performers, is "so opaque that there is no way to know how much may be lost to mismanagement."

Nigeria's finance ministry did not immediately return a request for comment. However, the Minister of finance, Kemi Adeosun has begun an internal sanitation of kept records while introducing new codes of conduct.

Money from the excess crude is occasionally used by the government to cover budget shortfalls.

In such cases, the money is shared between the federal, state and local governments.

Nigeria also runs the Nigeria Sovereign Investment Authority, with about $1.25 billion under management, but NRGI said it had ranked the ECA due to its larger balance sheet.