The Nigeria-São Tomé Joint Development Zone (JDZ) is claimed by both Nigeria and São Tomé e Príncipe. The two countries agreed in 2001 to enable oil exploration and jointly develop resources within the JDZ. This includes acreage on the southern fringe of the prolific Niger Delta basin in ultra-deep waters. The first well, in 2006, discovered the Obo field; whilst this is close to producing fields across the Nigerian maritime border, appraisal drilling has been disappointing and the field is classified as sub-commercial. Although drilling success rates in the basin have been high, discovered volumes have not met with early expectations, being gassy and smaller than anticipated. However, just seven wells have been drilled to date, and large areas of the basin remain unexplored. Nevertheless, results to date, combined with the current low oil price environment, potentially high development costs and challenging fiscal terms are likely to limit exploration in the immediate future.