Biocides are used to control problematic microorganisms in the oil and gas industry. High doses of biocides cause environmental and operational problems. Therefore, using biocide enhancers to make biocides more effective is highly desirable. 2,2-dibromo-3-nitrilopropionamide (DBNPA) is a popular biocide because it is broad-spectrum, effective, kills microorganisms immediately upon addition, and it degrades rapidly. D-amino acids are natural chemicals that have been used in lab tests to enhance biocides to treat biofilms. In this work, D-tyrosine was used to enhance DBNPA against Desulfovibrio vulgaris biofilm on C1018 carbon steel. After 7 days of incubation, the weight loss of coupons without treatment chemicals in culture medium was found to be 3.1 ± 0.1 mg/cm2. With a treatment of 150 ppm (w/w) DBNPA, the weight loss was reduced to 1.9 ± 0.1 mg/cm2 accompanied by a 1-log reduction in the sessile cell count. The combination of 150 ppm DBNPA + 1 ppm D-tyrosine achieved an extra 3-log reduction in sessile cell counts and an additional 30% reduction in weight loss compared with 150 ppm treatment of only DBNPA. The combination also led to a smaller maximum pit depth. Linear polarization resistance (LPR), potentiodynamic polarization and electrochemical impedance spectrometry (EIS) tests corroborated the enhancement effects.