A council has been told it must publish more details about a £500m contract for an incinerator project.
Gloucestershire County Council signed a contract with Urbaser Balfour Beatty for the scheme near Gloucester in 2013.
The Information Commissioner has ruled some parts of a previously redacted report, released under Freedom of Information rules, must be revealed.
It means the public will learn of some financial aspects which the council said were commercially sensitive.
Included in that are figures such as the price per tonne agreed with Urbaser Balfour Beatty (UBB) and the price to third parties of electricity generated by the incinerator.
Campaigners had argued that without this information it was impossible to properly judge whether the council had obtained value for money.
Gloucestershire County Council said it had complied with all previous requests from the commissioner, "however the legislation and guidance is unclear".
A council spokesman said: "We have to make sure we balance the needs of our contractors for commercial sensitivity with the desire to provide as much information as possible into the public domain.
"It is important for us to make sure that we get the best possible deal for Gloucestershire tax payers. There are details in the contract and the report which could undermine our ability to do this."
The report by accountancy firm Ernst and Young looked into the viability of the project before the contract was renegotiated in 2015.
The council has been given 35 days to disclose the information.
The project, at Javelin Park near junction 12 of the M5, met with fierce opposition and was only approved following a public inquiry.
It was originally refused planning permission by the county council and an unsuccessful bid by Stroud District Council to stop it being built reached the High Court.
Work on the project began in 2016 and the incinerator is due to begin operating next year.
The council claimed it would save taxpayers more than £100m over 25 years, power 25,000 homes, and "help us to reach our aim of 70% recycling across Gloucestershire".