| Amounts in US$ '000 | | Total | | |
| Exploration wells at 31 December 2015 | | | 22,906 | |
| Additions | | | 15,088 | |
| Write-offs | | | (19,949) | |
| Transfers | | | (9,795) | |
| Exploration wells at 31 December 2016 | | | 8,250 | |
| Additions | | | 35,299 | |
| Write-offs | | | (3,664) | |
| Transfers | | | (29,281) | |
| Exploration wells at 31 December 2017 | | | 10,604 | |