Apache Corporation senior project adviser Alex Ferguson said he was "shocked" at TAG Oil's use of the phrase "Texas of the south" in relation to East Coast oil prospects.
TAG Oil used the phrase in a report to North American investors, who were also told TAG planned to expand its exploration programme.
Apache has entered into a profit-sharing venture with TAG, which has exploration permits onshore in the East Coast Basin. Apache will invest up to US$100 million ($126 million) for a four-year exploration programme.
Mr Ferguson said it was too early to get excited over a possible commercial oil strike.
"We have done this before, and failed in other places, so we have seen the down side of getting too hyped about opportunities," he said.
GNS exploration geophysicist Chris Uruski said TAG Oil's assessment of the East Coast's potential was accurate but it was important not to have unrealistic expectations.
"It is and it isn't [accurate]. It is leaking oil and gas, that's for sure.
"We know that there are around 300 oil and gas seeps up and down the East Coast onshore," he said.
But unleashing that potential would be the challenge.
"As far as it being the Texas of New Zealand is concerned, that's probably overstating the case really, in my opinion."
This month explosive charges were due to be detonated as part of the mapping programme and exploratory wells were due to be drilled in April.
The areas of greatest interest at the moment were on the boundary of Hawke's Bay and Horizons regional councils and the border of the Gisborne district.
Wellington-based consultant geologist David Francis said the shale formations in the East Coast Basin were similar to those that produced oil and gas in North America.
Mr Ferguson said the exploration process was at an early stage and no decisions would be made about an expanded drilling programme until there was clear evidence of a commercial oil find and all stakeholders consulted.
The "Texas of the south" claim comes as the Government looks to make significant changes to the Crown Minerals Act next year to make it easier for companies to find and extract natural resources.
Energy and Resources Minister Phil Heatley said the Government was planning to make it easier for miners to explore and then extract minerals.
"We're going to make significant changes to the Crown Minerals Act because conversations to date under previous ministers have found that there are opportunities to improve the way that companies can access our minerals, apply for opportunities to explore, that type of thing," Mr Heatley said.
The Government planned to "get the best out of natural resources" to create jobs and lift the economy but was also "very, very conscious of our environmental obligations".
Labour's Energy spokeswoman, Moana Mackey, said the TAG announcement showed the Government's "drill it, mine it, sell it" approach to economic development was well under way. "This is not where New Zealand's economic future lies. We need to be investing instead in renewable solutions."
Mining industry group Straterra's chief executive, Chris Baker, said New Zealand needed a regulatory regime that was "competitive" with other countries to attract mining industry investment.
Ms Mackey questioned whether hydraulic fracturing or "fracking" was part of TAG Oil's plans for the East Coast. Fracking involves injecting high-pressure water, sand and chemicals into rock structures to crack them open and keep them open, releasing natural gas.
TAG and Apache are veterans of the controversial practice.
Apache has said the target on the East Coast was conventional oil "plays" but it could possibly target gas in the future.
An existing gas pipeline already passes through petroleum-bearing areas in Hawke's Bay.