US oil company Conoco was this week meeting loss adjusters in an attempt to assess the damage caused by the explosion which ripped through its refinery at Killingholme, on the Lincolnshire coast.
Crawford & Company, the world's largest risk and claims management group, has been appointed to handle claims at the plant, Conoco's largest in Europe.
A Conoco spokesman said a number of insurers were involved in the risk through the international insurance market.
He said: “It's very difficult to make any assessment of the losses at the moment.”
A spokesman for Crawford said no reason had yet been established for the blaze, which caused no major injuries.
All 199 people on the site have been accounted for, with just one person taken to hospital with minor cuts and burns. Apart from two units, all were shut down after the blast.
An internal inquiry has been launched with the Health and Safety Executive.
The plant normally produces 200,000 barrels of oil a day, accounting for more than 10% of total refining capacity in the UK.