Efforts to contact both businessmen for comment were unsuccessful.
According to the Oxfam research, the richest 1 per cent of Kiwis have 20 per cent of the wealth in New Zealand, with 90 per cent of the population owning less than half of the country's wealth.
Rachael Le Mesurier, executive director of Oxfam NZ, said the organisation was shocked to discover such a level of wealth inequality.
"The gap between the extremely wealthy and the rest of us is greater than we thought, both in New Zealand and around the world. It is trapping huge numbers of people in poverty and fracturing our societies - as seen in New Zealand in the changing profile of home ownership."
Oxfam's research draws on data from the Credit Suisse Global Wealth Databook and the Forbes list of billionaires, and examines the wealth of people - not their disposable income.
The full report to be released today - An economy for the 99 per cent - is part of an annual series.
Finance Minister Steven Joyce said the comparison of Hart and Chandler with everyone else in New Zealand was "a bit nonsensical", because they had mostly accumulated their wealth overseas by running successful businesses.
"The aim for a country like New Zealand is to encourage more Kiwis to be successful on the world stage, whether in business, sport or in world organisations.
"The way we do that is make sure that we provide the best possible start for our young people through providing a quality education and investment in social services."
Joyce said it was important to note the latest OECD data showed that income growth for the bottom 10 per cent of earners in NZ has been the second fastest in the OECD since 2010. That didn't include increases to benefits, he said.
Labour leader Andrew Little cited home ownership rates as the "New Zealand measure of inequality". Nationwide 63.2 per cent of people today live in their own homes - the lowest rate since the 61.2 per cent recorded at the 1951 Census.
"Until we see that rising, then we cannot say that we are addressing the inequality problem," Little said.
Oxfam's previous reports have been criticised by some think tanks, and Dr Eric Crampton of the New Zealand Initiative said caution was needed in assessing the population with lowest share of wealth in countries like New Zealand.
That was because many graduates' student debt would count against them - meaning a new doctor could count as poorer than families experiencing hardship but with less debt.
Crampton said the share of the world's population living in absolute poverty is lower than it has ever been.
It was appropriate to focus on wealth inequality in corruption-ridden countries with "tinpot rulers", he said, but elsewhere people become wealthy by producing goods and services that are valued.
"Bill Gates becoming a dollar richer immiserates no one . . . Oxfam tells us nothing new in revealing that New Zealand's top one per cent own about 20 per cent of all wealth - similar figures were released by Statistics NZ last year, and showed that New Zealand's wealth concentration is pretty middling in OECD rankings."
Crampton said inequality's "real bite" in New Zealand was because of a broken housing market, with the rising cost of housing especially hurting the poor. The initiative has called for a revamping of zoning rules, including the abolition of Auckland's rural urban boundary.
Oxfam's findings
• Research by Oxfam has put the wealth of New Zealanders Graeme Hart and Richard Chandler at US$6.4 billion and US$2.7 billion respectively.
• Oxfam says that means they own more wealth than the poorest 30 per cent of the adult New Zealand population.
