Shares in New Zealand Oil & Gas fell 2.5% on Thursday after the company said it was writing off the rest of its investment in Pike River Coal.
Twenty-nine men were killed in explosions at the West Coast mine in November 2010. The company was put into receivership the following month.
New Zealand Oil & Gas, which owns 29% of Pike River Coal, says it has been told by the receivers that there are now three possible sale options.
The mine could be sold outright; the sale might be a structured deal with a smaller upfront payment then payments at certain milestones; or only the mine's removable assets might be sold.
New Zealand Oil & Gas is writing off the rest of its investment in Pike River, because it doesn't know how much money it will get back from the sale nor when the deal will be done.
The move will increase its writeoff provisions by almost $21 million in the final six months of 2011.
Shares in New Zealand Oil and Gas fell 2 cents to 74 cents on Thursday.