Stewart Whyte, managing director of consultancy Fleet Audits, told an audience at the Fleet News UK Congress that most companies were well informed and passed on the information to their drivers.
Whyte said: 'Many employers are anxious to co-operate and provide information, and weren't helped by the SMMT CO2 website being unaudited for a year.
'As awareness is increased, more employers will realise that it is in everyone's interests to understand the changes. But there will always be the 'untouchables' who don't read Fleet News or are not members of ACFO who don't realise what's coming.'
He added that a significant number of drivers in medium sized cars with a typical CO2 emissions rating from 185 - 220g/km probably would not know whether they are paying any more or less tax than under the present system.
Whyte also criticised forthcoming changes to Inland Revenue approved mileage rates (IRAMR), because it included an element of reward for higher mileage.
He said: 'It encourages people to do more miles and this doesn't help the environment, and overgenerous payments provide a perverse incentive to cover more business miles.'