LONDON, May 14 (Reuters) - Nigeria's state oil firm NNPC has issued crude export contracts that are expected to last two years instead of the usual one year, trading sources familiar with the matter said on Monday.
A partial preliminary list showed 30 companies including the world's largest energy traders Vitol, Trafigura and Glencore.
The final list could contain between 50 to 60 companies, the sources added.
NNPC did not immediately respond to a request for comment.
The list has emerged later than usual.
In 2017, NNPC published results in January awarding contracts to 39 companies.
Other companies included in partial 2018 list are Total, Spain's Cepsa, the trading arm of Azerbaijan's Socar and Lukoil's trading subsidiary Litasco.
Switzerland-based Mocoh and Petraco, Lebanon's BB Energy and Nigerian firms Sahara Group, Eterna and Oando were also among those on the list.
Reporting by Julia Payne, Amanda Cooper and Libby George in London Additional reporting by Alexis Akwagyiram in Lagos Editing by Mark Potter and Edmund Blair