The present invention discloses a gasoline efficacy promoter (GEP) boosting combustion efficiency of gasoline in internal combustion engines by a mechanism of micro-dissociation comprising a microemulsion of modified bio-carbon, a surfactant, water, a modified vegetable oil and a dispersant, and a method of making it. The gasoline efficacy promoter, environmentally friendly and stable for longer than six months, can increase the combustion efficiency by more than 10%, and reduce 80% of NOx formation in exhaust emission when an appropriate dosage is added to a fuel tank in a vehicle.