Phosphatidylethanol (PEth) is increasingly used as a biomarker of heavy drinking. Many different forms of PEth can form in red blood cell membranes from the action of the enzyme phospholipase D. PEth has a very long duration in blood because, in contrast to other tissues, RBCs lack the enzymes that degrade PEth. Because this biomarker is relatively new, interpretations of the analytical measurements of PEth may be misinterpreted and the resulting predictions of actual alcohol consumption inaccurate. Hence, a simple pharmacokinetic model of PEth was developed to provide a means of contextualizing these analytical results. A number of alcohol consumption scenarios and current clinical screening levels were examined with the model.