Researchers tend to use oral- and silent-reading fluency measures interchangeably and to generalize research findings across reading modes, especially from oral to silent reading. In this study, we sought to examine if oral and silent word-reading fluency rely on the same cognitive-linguistic skills. Three hundred and forty-five Greek children (80 from Grade 2, 85 from Grade 4, 91 from Grade 6, and 89 from Grade 10) were assessed on measures of general cognitive ability, speed of processing, phonological awareness, rapid automatized naming, orthographic knowledge, articulation rate, and word-reading fluency (oral and silent). Results of hierarchical regression analyses revealed that phonological awareness was a unique predictor of both reading outcomes in Grade 2 and orthographic knowledge was a unique predictor of both reading outcomes in Grades 4, 6, and 10. However, rapid automatized naming predicted only oral word-reading fluency. These findings suggest that silent and oral word-reading fluency do not necessarily rely on the same cognitive-linguistic skills at the same grade level and we need to exercise some caution when we generalize the findings across reading modes.