Octane Plus. A highly efficient fuel treatment for adding to all commercially available petrol to increase octane ratings. Ref: 14 A highly efficient fuel treatment for adding to all commercially available petrol to increase octane ratings. Price: £5.21 (Including VAT at 17.5%) Size 250-ml (£4.43) Specification Proven over 20 years. Maintains catalyst efficiency by scavenging 'front end phosphorous'. Fully compatible with oxygenates, ethanol containing fuel and MTBE treated fuels. Quantity: