Opponents of a Pacific-wide trade deal say the promised gains have been wildly overstated, and there is unlikely to be any benefit to New Zealand.
Last year Trade Minister Tim Groser said the Trans Pacific Partnership or TPP would deliver economic gains of $5 billion by 2025.
But Wellington economist Geoff Bertram said the findings are flawed and would not stand up to intellectual analysis.
Dr Bertram told Morning Report about a quarter of the claims made in favour of the deal made sense and the rest have been plucked out of thin air.
He said this deal is quite unlike the Free Trade Agreement with China which yielded real benefits.
In the past, supporters of the TPP have argued freer trade are of benefit to New Zealand and the country cannot afford to be left out of an agreement involving two of the world's three largest economies.