Vector has received unsolicited interest in its gas transmission and non-Auckland gas distribution businesses, it says.
The electricity and gas company said it was always looking to maximise shareholder value, and has now hired Goldman Sachs to assess future options for these businesses.
Vector said it would update the market with any relevant developments.
Forsyth Barr energy analyst Andrew Harvey-Green said a sale could be a good move for the network operator, although these were important strategic assets.
"There would be a loss of synergy if those assets were sold."
Vector sold its Wellington electricity network business for $785 million in April 2008.
Mr Harvey-Green said Vector saw itself as an Auckland-focused business.
"From that perspective you can see why [Vector] might view its gas transmission and non-Auckland gas distribution businesses as not central to their underlying business."
Vector's overall gas transportation business contributed $96.1 million of revenue in the six months to December, a fall of 9 percent on the year earlier period.
Underlying profit fell 14 percent from $67 million to $57.5 million.
Capital expenditure in the gas transmission business rose 35 percent to $23 million, due to an increase in a new connections in the fast growing Auckland market and transmission relocations.