The research conducted by TomTom Business Solutions found 57% of drivers have over-estimated their mileage when claiming expenses, with 25% doing so regularly.
Companies and their employees are required by law to keep accurate mileage records for Benefit in Kind tax compliance, but more than a third (35%) of respondents have never been challenged by their employers over the accuracy of their claims.
"It is worrying that such a large proportion of Irish business drivers are over-estimating mileage claims because it exposes their employers to serious legal consequences," said Giles Margerison, Director UK and Ireland for TomTom Business Solutions.
"Irish businesses are required to maintain comprehensive records for all trips undertaken, including start and destination details, the number of kilometres travelled and the nature of all business journeys."
The research, conducted among company drivers not using an automated mileage recording system, revealed 82% of drivers find recording and submitting mileage a laborious process.
For almost a quarter (23%) of those questioned the process takes at least eight hours each month, with 82% losing in excess of two hours.
Paper proved to be the most popular format for keeping mileage records (36%), while 17% of drivers record and submit records via their computer.
"Antiquated systems for recording mileage mean many businesses are suffering a significant blow to productivity, which could run to more than 800 hours a month for companies employing 100 drivers," added Margerison.
"This lost productivity can have a major impact on a company's ability to remain competitive in an increasingly challenging economic environment. Advanced fleet management technology helps to simplify the mileage registration process, allowing businesses to guarantee the accuracy of records and maximise efficiency."