An LP Gas Association survey of 16 insurance companies found the firms would cover gas-powered vehicles without forcing drivers to pay increased premiums.
The survey, backed by the Association of British Insurers, found that the AA, Direct Line and Norwich Union were among the companies that would treat 'green' drivers the same as their petrol counterparts.
But fleets must tell insurance companies whether the conversion is manufacturer approved or fitted after the car left the factory, an LP Gas Association spokesman said.
'At the moment, about 90% of LPG vehicles on UK roads are aftermarket conversions. As with any vehicle modifications, it is imperative that the vehicle owner informs their insurance company of the conversion to LPG,' he added.