The Motor Medic M5012 Lead Substitute is typically used at a ratio of one 12 oz bottle per 20 gallons of gasoline. For 1 gallon, you would need 0.6 oz of the lead substitute to maintain the recommended concentration. Since you're blending 1 gallon of 100 octane leaded fuel to achieve 97 octane, the exact amount of lead substitute needed depends on the fuel composition and blending ratios. If you're aiming for precise octane adjustments, using an octane blending calculator or consulting a fuel specialist might help fine-tune the mix. Let me know if you need help with anything else!