In order to maximize online reading performance and comprehension, how should a designer choose typographical variables such as font size and font type? This paper presents an eye tracking study of how font size and font type affect online reading. In a between-subjects design, we collected data from 82 subjects reading stories formatted in a variety of point sizes, san serif, and serif fonts. Reading statistics such as reading speed were computed, and post-tests of comprehension were recorded. For smaller font sizes, fixation durations are significantly longer, resulting in slower reading – but not significantly slower. While there were no significant differences in serif vs. san serif fonts, serif reading was slightly faster. Significant eye tracking differences were found for demographic variables such as age group and whether English is the subject’s first language.