Viridor and the Waste Recycling Group (WRG) are both bidding to buy Shanks landfill assets.
In a company statement released this week, the Shanks Group said it had been discussing the sale of its landfill assets including sites and gas assets to the Pennon Group, which operates Viridor Waste, for some months.
Shanks operates 20 landfill sites around the UK. Press reports value the sites at £200 million.
These discussions are continuing and are at an advanced stage, although there can be no certainty that they will lead to such a sale, said Shanks.
But during the course of discussions with Pennon, Terra Firma, which owns WRG, also approached Shanks.
Initially Terra Firma had wanted to impose pre-conditions, which the Shanks board rejected. The pre-conditions included underwriting its costs and entering into an eight-week exclusivity period.
However, since the rejection, Terra Firma has re-approached Shanks, removed the pre-conditions, and improved the indicative price.
Shanks company announcement said: There is uncertainty over whether Terra Firmas approach would lead to a binding offer for the landfill assets and, if it did, what the consideration and contractual terms would be.
The company said it would make an announcement when appropriate.