NZOG shares finished the day up 3 cents (3.87%) at 80.5 cents.
New Zealand Oil and Gas, which owns 15% of the Kupe oil and gas field off the Taranaki coast, says preliminary results of a review of the field's reserves suggest estimates of what remains may need to be increased.
The listed company says the information is being independently-reviewed by all parties, and they hope to make a detailed announcement about their position in mid-July.
The Kupe field is half owned by Origin Energy, state-owned power company Genesis Energy holds 31% and Mitsui 4%.
In July 2010 the field's owners raised their estimates of the field's reserves by 6%.
