Associate Energy Minister Harry Duynhoven announced the offer this morning, saying it was one of the largest onshore Taranaki blocks offers in over 20 years - nine blocks representing a total area of about 3273 square kilometres.

He said the large area had been aggregated to provide explorers with blocks of material size that contained a broad range of exploration opportunities.

"The size of the blocks and their underlying prospectivity has already attracted interest from a variety of local and overseas exploration companies," Duynhoven said.

"Some of these companies bring with them the type of experience required to unlock the deep gas plays that are considered to be underexplored."

Duynhoven said the blocks offer was being supported by a large and modern technical data package that would be made freely available to prospective explorers.

As the government had aggregated such large areas, in return it expected explorers to propose aggressive work programs to explore this proven petroleum acreage.

"A fresh approach, which adopts latest technologies and concepts to explore the variety of play types from shallow oil deposits to deep gas to unlock the potential of this productive basin, is expected," Duynhoven said.

Onshore Taranaki is New Zealand's only commercial petroleum province, with exploration efforts dating back over 140 years.

The basin contains a thick Cretaceous-Tertiary sedimentary sequence. Presently worked plays include the Miocene-aged submarine fan systems, Eocene fluvial-deltaic graben fill, and Miocene-Pliocene buried volcanic edifices. Drilling to date has targeted anticlinal or four-way dip closures, but these vary considerably due to the region's complex tectonic history.

The onshore-offshore Taranaki Basin has seven producing gas-condensate and oil fields. Crown Minerals, organiser of the offer, says these fields have recoverable reserves (P50) of 183 million barrels of oil and condensate and 2.16 trillion cubic feet of gas.

Duynhoven said that while the New Zealand Energy Strategy emphasised a renewable energy future, it also recognised that more gas needed to be found to fuel current gas-fired baseload power stations and peaking plants, as well as industrial and residential uses.

Bids for the Onshore Taranaki Basin Blocks round close next May 30.