The CI Co-Op is the new provide of fuel for a number of States departments.
The new deal was agreed in December 2023.
The States say it will 'offer better value for money and more flexible locations for filling up.'
Currently it applies to vehicles run by Guernsey Water, Health and Social Care and Education's Pupil Transport Service.
Previously, these departments had used a locally run garage.
It's unclear whether the agreement covers States Works, which operates a large and diverse fleet.

"Tropical nights" forecast for the Channel Islands
Guernsey rabbits at risk from two deadly diseases
Exhibition to celebrate 90 Years of Guernsey's Ambulance Service
Guernsey sewage pipe repairs "unlikely to be a quick"
Guernsey FC to fight for promotion at Victoria Park
Move to return St Julian's House to Guernsey's emergency shelter
Jersey and Guernsey included in UK-Gulf trade deal
St Pier says States put investigation before his experience in P&R seat vote