Laboratory biocide effectiveness testing is an important step in microbiologically influenced corrosion (MIC) management because it offers a controlled environment where numerous variables such as biocide type, concentration, and application method can be investigated for their effects on microbiological populations and corrosion rate. In this paper the results of biocide testing performed for a crude oil pipeline system are presented. Experiments were performed using biofilms grown from water collected from the pipeline system and comparisons were made between samples where no biocide was added and biocide addition at two different concentrations. The effects of the biocide were evaluated using corrosion rates, planktonic and sessile populations, and activity. A key finding from the experiments was that the addition of biocide resulted in an increase in general corrosion rates and pitting rates. These results further emphasize the need to consider the effects of biocide on corrosion and not just microbiological populations and that biocide addition could result in unintended and unexpected consequences.