Shares in UK Coal are set to rise amid reports its property portfolio is worth £300m more than previously thought.
UK Coal is looking to develop its land portfolio
The country's largest coal producer believes its 50,000 acres of land is worth "well in excess" of £500m, the Independent on Sunday says.
UK Coal's last estimate put the value of land - primarily surrounding active and closed mines - at £274m.
It is expected the firm will seek to get planning permission for much of the land, and sell it to developers.
Profits from the sales will be used to increase production at its mines, the report said.
UK Coal, formerly known as RJB Mining inherited the land during the privatisation of coal industry in 1994, and most of it is so-called brown field sites, close to urban centres.
The firm's finances have improved in recent years and it made a £7m profit in the first six months of 2006.
But reduced output at four deep cast mines over the summer will force it into the red for the year as a whole.
The Doncaster-based firm wants to cut its reliance on coal, and got approval for its first wind farm last year.
UK Coal supplies 7% of the country's electricity needs and employs 4,000 staff.
It operates deep cast mines in Northumberland, Yorkshire, Nottinghamshire and Warwickshire.