The author of a report into the environmental effects of more drilling in the Maui gas field, says Shell Todd Oil has not given him enough information to give a full assessment.
The report was commissioned by the Environmental Protection Agency for a hearing into whether the company will be allowed to continue extracting gas from the field off the coast of Taranaki.
The potential negative effects on the seabed, water quality and marine plant life are among the aspects considered by the report.
It said most would be negligible but some had the potential to be moderately adverse.
But the report's author, marine biologist Matthew Jury, said there was some uncertainty in the assessment because Shell did not give enough information.
For example, he said Shell had not applied a rigourous enough standard to its assessment of the risk to fish and marine mammals.