A FRESH petrol price war could ignite tomorrow in time for the long weekend when a new On The Run service station sells unleaded for 99c a litre.

On The Run will offer the discount price at its new Dry Creek service station, just off Salisbury Highway, from 10am until 2pm tomorrow.

On The Run general manager Michaela Webster said the promotion could be handy for travellers heading away for the long weekend.

"We thought Adelaide would appreciate some relief on costs over the long weekend," she said.

"We're trying to get some excitement happening about the weekend in general."

When Mogas ran a 99c a litre petrol promotion at its Brooklyn Park service station last month it prompted other nearby service stations to slash their prices.