An understanding of the relationship between chemical structure and lubricant performance is highly desirable from both a fundamental and a practical perspective, such knowledge being vital to improve the performance of mineral oils and to guide the design of future synthetic lubricants. The rheological properties of alkanes of intermediate molecular size (C-20-C-40) are of particular interest as they form the main constituents of lubricant basestocks. In this work, we determine the viscosity number (VN) for a number of alkanes in the mass range of interest by molecular simulation, Quantitative agreement with experimental data for all systems studied is achieved, further illustrating the value of molecular simulation in predicting lubricant properties and its potential for providing guidance in the design of synthetic lubricants with desired properties.