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.
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