Purpose: This study investigates how the increased use of part-time and nontenure-track instructors may result in grade inflation. Design/methodology/approach: This research uses ten years of registrar data at a Midwest State (USA) institution to perform a multiple regression grade analysis. Findings: Evidence is found that part-time and nontenure-track instructors give higher grades even after accounting for many alternative explanations for grade differences. Research limitations/implications: The source for the data used for the study is one public institution. Additional studies from a wider range of institution types would be necessary before more definite conclusions can be drawn. Originality/value: This paper extends the work performed by a number of other authors by analyzing a significantly longer-time period and by using data not specific to a particular discipline. In addition, this study expands upon past studies by including full-time nontenure-track faculty whose numbers are increasing rapidly in higher education. A multiple regression analysis is also used that provides for more robust results and controls for many alternative explanations of grade differences. (Contains 3 tables.)