Industry sources say cash set aside by two major coal firms before they collapsed amounts to a quarter of the sum now needed to restore scarred landscapes.
It means most of the mines in East Ayrshire, Lanarkshire, Dumfries and Galloway, Fife and Midlothian are likely to stay derelict, or to be cleaned up on the cheap.
The revelations have prompted anger from politicians, environmental groups and local communities.
The falling price of coal forced Scottish Coal into liquidation in April. Opencast firm ATH Resources was wound up in May. The collapses threw the future of 32 opencast sites into doubt.
The sites were meant to have insurance bonds in place to ensure the cost of restoration could be met, but the bonds were inadequate, had expired or did not exist.
Now it has emerged the gap between the money councils have and the money they actually need for clean-ups is much higher than previously estimated.
Around £66 million is available for restoration likely to cost £255m. Rising costs are likely to raise the gap to £210m, experts say. Green MSP Patrick Harvie said it was a "national scandal" for which the coal companies must be held to account.
In East Ayrshire, where 22 sites face a £132m shortfall, council chief executive Fiona Lees called the council's funding gap "notional". She said: "It has never been suggested this amount or anything like it be spent by the council and so alternative restoration proposals are being developed."