Premium gas has higher octane rating than regular. A VW Jetta should be run on premium as they're designed for it. Octane rating is the 'anti knock' rating of a motor.As the compression ratio is raised, so a motor tends to 'knock' or pre-ignite the cylinder charge.remium gas has higher octane rating than regular. A VW Jetta should be run on premium as they're designed for it. Octane rating is the 'anti knock' rating of a motor.