Quantifying biofilm-associated microbes is of great importance in the oil and gas and pipeline industries where biofilms remain one of the largest contributors to corrosion yet to be fully understood. Bacteria and Archaea are known to be associated with microbially-influenced corrosion (MIC). Microbes cause corrosion through multiple mechanisms both directly and indirectly. Directly microbes can attack through the consumption of electrons from the iron or creating differential concentration cells on the surface of metals or passivating metal surfaces by forming a complete biofilm layer over the entire surface. Indirectly they produce corrosive agents such as hydrogen sulfide or through attack and removal of protective coatings. Given that microbes can passivate steel surfaces biofilms have been reported as both causative agents of corrosion and protective agents under different environmental conditions. This illustrates the lack of knowledge surrounding biofilms and MIC: what role is the biofilm really playing and what is its contribution to corrosion? Many commercially available protocols are used to measure planktonic bacteria and assess MIC risk. Methods also exist to quantify biofilm initiation (cell attachment) growth and fully mature biofilms. However there is yet no quantifiable correlation between planktonic cell counts biofilm development and corrosion rates. It is of great importance to industry to be able to easily and accurately quantify biofilm-associated cells and understand how this impacts corrosion rates.Here we study the initiation of biofilm growth in terms of biofilm-associated cells of single-species biofilms with respect to planktonic inoculation concentrations. An aerobic soil species (Pseudomonas fluorescens) capable of rapid biofilm formation and an anaerobic species (Geoalkalibacter subterraneus) known to be in association with oil pipeline corrosion were studied using theCalgary Biofilm Device™ with sonication disruption and CFU plate counting along with confocal imaging. Current results indicate that for P. fluorescens and G. subterraneus a minimum concentration of planktonic cells are required to initiate biofilm formation then biofilms reach a maximum CFU count. Following biofilm formation and maturation the concentration of biofilm-associated cells remains constant regardless of the planktonic cell concentration. These results demonstrate that an established biofilm will reach a steady-state cell concentration where biofilm-associated cells remain constant regardless of planktonic cell densities. This finding has great significance for the oil and gas industry; as it suggests that traditional planktonic cell counts are an inaccurate methodology and completely irrelevant indicator of estimating microbial numbers affecting corrosion on the steel substrate. This may lead to inaccurate risk assessments of microbially influenced corrosion.