Treasury documents showed the operating deficit for the five months ended November was $2.3 billion lower than expected at $2.5 billion, due mainly to the Cullen fund recording gains above forecast of more than $1 billion.
The gains were from investments and other derivatives in strong global equity markets.
The fund has $17.4 billion under management. The Government stopped paying into the fund when it was elected in 2008, saying it could not afford to borrow to pay into the fund.
Prime Minister John Key announced on Wednesday that Treasury had been asked to advise on the partial sale of four energy companies - Genesis Power, Meridian, Mighty River Power and Solid Energy. Treasury had also been asked to review the Government selling down some of its majority stake in Air New Zealand.
A partial sale could raise between $2.4 billion at a 25% stake of $4.8 billion at a 49% sell-down.
Mr Key said that borrowing $300 million a week was unaffordable and was holding the economy back. If the assets were sold, the money would be used to reduce borrowing and debt.
The Government planned to reduce new spending in the Budget to around $800 million to $900 million, down from the $1.1 billion announced last year.
The Government owned $220 billion of assets across a range of social, financial and commercial investments - everything from hospitals, roads, prisons, schools and police stations to the super fund, electricity companies and coal mining operations.
Another $33 billion of net new assets were expected to be bought during the next five years.
"At the margin, there are two ways we can acquire these new assets: either we can borrow more or we can change the mix of assets we own. The Government can't keep building up debt indefinitely."
Mr Key suggested that the super fund could be one possible investor in any partial sale of assets.
At the end of November, the fund had $273 million invested in Auckland International Airport, $124 million in Fletcher Building, $92 million in Contact Energy, $91.5 million in Telecom, $44.5 million on Sky City Entertainment, $39.4 million in Fisher and Paykel Healthcare, $38.1 million in Sky Network Television, $36 million in Infratil, $22.7 million in Guinness Peat Group and $21.6 million in Ryman Healthcare.
The fund also has substantial investments overseas.
Labour finance spokesman David Cunliffe earlier told the Otago Daily Times Labour would resume the payments into the fund, reckoning that the returns would offset borrowing costs.
Fitch Ratings said Mr Key's plan to slash spending and sell stakes in some assets could improve the sustainability of the public finances, but high household borrowing remained a big concern.
A rating downgrade was still possible unless there was clear evidence of rebalancing of the economy, Dow Jones Newswires reported.
Fitch sovereign analyst Andrew Colquhoun said that without clear evidence of a rebalancing, Fitch remained "more likely than not" to downgrade the rating within its usual outlook horizon during the next 18 months or so.
Fitch has a negative outlook on its AA+ foreign currency long-term credit rating on New Zealand.
