The country's largest fuel retailer says the Commerce Commission is putting it to work, with substantial requests for confidential information.
Z Energy chief executive Mike Bennetts, said the competition watchdog had requested information dating back 10 years, including internal correspondence, for its fuel market study.
"We can do it, but, it is a heck of a lot of work and a heck of a lot of data," he said.
"It indicates the commission are being very, very thorough in not just what they are examining but the depth to which they examine things."
The information was due at the end of March, Mr Bennetts said.
The law was changed last year to give the commission power to launch market studies, with the fuel industry its first target.
Companies have responded to 40 preliminary questions so far, including queries about increased margins and how market structure and refining interests affect competition.
The final report, determining if the market is providing good outcomes for motorists, will be published in December.