The Luton-based operator is using the system to improve driving style, with real-time monitoring of drivers and vehicles.
The system also records personal and business mileage, delivering accurate data for expense claims and full compliance with HMRC vehicle mileage management policy.
Mimram has issued drivers with PDAs, linked to the system, giving it a fully integrated solution for managing, scheduling and communicating with its mobile workforce.
Mimram's Gary Price describes it as a "real peace of mind tool", adding: "We've been given a top rate service and valuable data to help steer our business and fleet.
"The results we've had on driver behaviour have been excellent and in the future ... we're hoping to do more with fuel consumption to see how we can reduce that further," says Price.
"We've made a 10% saving on fuel so far and that's something we're confident we can reduce further with Masternaut."