The Nigerian National Petroleum Corporation (NNPC), Nigeria's state oil company, has lifted a ban on over 100 vessels due to suspected oil theft, but asked ship owners last month to sign a letter of comfort to "guarantee to indemnify" it against any illicit use of their vessel.

This led some owners to reject pending bookings but Shell had no immediate comment.

However towards achieving this Royal Dutch Shell have today asked ship owners exporting its Nigerian oil to sign a "letter of comfort" (LoC) in order to be assured that its oil is not stolen, an email from the company seen by Reuters showed.

"Please be informed we expect LPG & Products ship owners to sign the NNPC LoC for any future Shell loading voyages," the email stated.