Paragon Car Finance questioned 255 fleet managers and found that 58% or respondents are concerned at the absence of restrictions on companies setting up as LPG-converters.
The survey highlights the importance of fleet managers using reputable converters if they are paying for aftermarket conversions so their vehicles can use alternative fuels whose pump price is half the price of petrol or diesel.
According to Transport Action PowerShift, which provides grants for companies converting to alternative fuels and monitors the standards of converters, more than 12,000 vehicles had been converted using its approved partners by the start of this year.
But Government figures estimate that by the end of the decade, up to 250,000 vehicles could be running on alternative fuels.
Paragon's survey also showed that 50% of fleets had changed their policy as a result of the launch of carbon dioxide-based company car tax, while 63% expected demand for opt-out schemes to increase following the launch of the tax.
The survey also revealed that more than half of companies had experience problems with new tax codes for drivers.
Fleet News reported earlier this year that a computer error at the Inland Revenue meant hundreds of thousands of drivers received the wrong tax bills this year, despite fleet managers providing all the information needed to ensure a correct statement was issued, under the new carbon dioxide-based tax regime.