Oil company PetroTal upgraded the reserves estimate for its key Bretana oil field in Peru.
Proven, or 1P, reserves had risen 4% to 22.3 million barrels, according to a year-end reserve evaluation by Netherland, Sewell & Associates.
Proven and probable, or 2P, reserves had risen 7% to 51.0 million barrels and proven, probable and possible, or 3P, reserves had risen 25% to 106.1 million barrels.
The asset's net present value was calculated at $317 million for 1P reserves and $830 million for 2P reserves.
At 8:54am: (LON:PTAL) share price was 0p at 8.5p