The operator of the Tui offshore Taranaki oil and gas field says probable reserves are between nine and 11 million barrels of oil short of the 50.5 million barrels previously thought.

World markets were up overnight, as positive debt reports came out of the United States and Europe.

The gloves have come off for the first time in the Pike River commission of inquiry, with Solid Energy chief executive Don Elder taking "great offence" at suggestions he is trying to lower the mine's value prior to sale.

The tone on Wall Street and Europe's equity markets remained positive overnight amid optimism the EU is making progress in its efforts to avert a Greek default.