Thales Group runs a fleet of LPG vehicles - including 144 Ford Escort vans, 77 Focuses, 28 Transits, two Vauxhall Vectras and two Astras - out of a fleet of 2,675 vehicles.
The company has 13 Calor Autogas bunkers at its sites, with a further four planned for early this year.
As part of its conversion to LPG the Thales Group has also taken full advantage of the Energy Saving Trust's PowerShift grants, receiving about £250,000 worth of grants in 2001 to pay towards the cost of LPG systems.
Thales Group fleet manager Nigel Rowden said: 'With group fuel costs of several million pounds per annum, exploring ways of reducing costs is a continuous exercise.
'We have already cut fuel costs by more than 50%, saving thousands of pounds a year on each vehicle converted to LPG. The decision to increase our bi-fuel fleet is an obvious one.'
The move to LPG also ties in the firm's accreditation to environmental standard ISO14001.
Rowden added: 'By installing on-site refuelling we are able to take advantage of further reduced fuel costs from Calor Autogas due to bulk purchasing. This cuts a further 20% to 30% off the retail forecourt price of Autogas, which is itself 50% cheaper than petrol or diesel.'
All Thales Group bi-fuel vehicles are currently sourced through either Ford conversion specialist Hendy Specialist Vehicle Operations or from Vauxhall via its conversion centre at Millbrook.