MSPs have approved a compensation scheme for BP, in case one of its key pipelines is damaged by the building of the new Forth Road Bridge.
The scheme, thought to be worth more than £100m, would kick in if the Forties pipeline is damaged.
The £2bn bridge, linking Edinburgh and Fife, is due for completion by 2016.
The Scottish Parliament's finance committee, which backed the move, discussed the issue in private for security reasons.
Discussions over the scheme have been taking place in secret over several months.
A spokesman for government agency Transport Scotland said: "The contingent liability is required to cover the extremely remote possibility as an insurance that the pipeline could be damaged as a result of the construction of the new bridge."
The spokesman added: "This is a potential liability to the contract not a cost, and as such does not increase the estimated cost of the project.
"The project remains on programme and on budget."
The finance committee agreed to hear the issue behind closed doors on the advice of the Centre for Protection of National Infrastructure, a security body, about the "strategic importance and sensitivity of the pipeline".
The Scottish Greens said it was "inappropriate" that MSPs were kept in the dark about the deal.
The new bridge, approved by MSPs last year, was brought forward in the wake of concerns about the condition of the existing road crossing, now more than 40 years old.
It has been described by the Holyrood government as the biggest Scottish infrastructure project for a generation, and vital to the economy.
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