Fixed grant levels for fleets converting to cleaner fuels will apply for all vehicle categories and will be taken from an overall grant fund of £658,000 issued by the Scottish Executive.
A spokesman at the EST, said: 'PowerShift and autogas+ grants exist to help support vehicle operators to clean up their fleets in a manner which is both effective and affordable.
The new fixed grant system for PowerShift Scotland is not only more transparent, making it clear from the outset what grant applicants will receive, but also easier to apply for.
'The changes have been made to ensure that the new system can continue to provide real cost and environmental benefits to the customer, assure stability for the market and ensure value for money.'
The autogas+ grants for the cost of converting to or buying a new bi-fuel vehicle remain unchanged at £800.
Liquefied petroleum gas (LPG) vehicles in emissions bands two and three are now also eligible under the autogas+ scheme for an £800 grant.