Okoro-2 follow up appraisal well was drilled in Nov 1974 by Japan Petroleum at the eastern extension of the field but it was water wet.

Amni International Petroleum Development Company Limited (AMNI) was originally granted oil prospecting licence (OPL) 469 on a sole risk basis on 24 August 1993 for a term of 5 years by Nigeria's Ministry of Petroleum and Mineral Resources as part of the Nigerian Government indigenous licensing programme.

As a result of the successful implementation of its work programme, OPL 469 was converted to Oil Mining Lease (OML) 112 for a term of 25 years in 1998.

A total of 70 feet (21 m) (True Vertical Depth) of net oil pay was encountered, which was greater than expected at this location.

As a result of the two well appraisal drilling programme, Afren enhanced the proved and probable reserves cases on the Okoro-Setu development.

In June 2006, Afren signed a Financing and Production Sharing and Technical Services Agreement with Amni for participation in the development of Okoro and Setu.

In April 2007, the Field Development Plan (FDP) was approved by the Department of Petroleum Resources in Nigeria and the partners secured a Floating Production Storage and Offtake Vessel (FPSO).

On 21 March 2007, Afren plc announced the signing of a fully underwritten US$200 million debt facility to finance the development of the Okoro – Setu project.

This is as a result of better reservoir quality than incorporated into the original field simulation model, good aquifer support and water breakthrough from the existing production wells occurring much later than predicted.