Solly said the Government would be doing very well if it got to 500,000 pre-registrations. "That would be a very good outcome."
He said anything above 500,000 would be surprising. But the big question then would be how many people would convert their interest into actually buying shares.
"These are good signals but they've got to convert yet."
Solly said there was a lot of information about the offer still to emerge and some who pre-registered might look through the documents and decide it was not for them.
Part of the pre-registration process involves indicating how much money people would be prepared to invest in Mighty River Power.
But the Government is staying mum on the exact level of interest.
A spokeswoman for State Owned Enterprises Minister Tony Ryall said it was not allowed to give a breakdown of the levels of investment indicated by pre-registration because that would breach securities law.
"Under securities law we are not allowed to talk about likely demand," she said.
The Mighty River offer document is expected to be available in mid-April with a listing set down for May.
Pre-register
People can pre-register at www.mightyrivershares.govt.nz or by calling 0800 90-30-90.