Complex (working memory) span tasks have generally shown larger and more consistent correlations with higher-order cognition than have simple (or short-term memory) span tasks. The relation between verbal complex and simple verbal span tasks to fluid abilities as a function of list-length was examined. The results suggest that the simple span-fluid abilities correlation changes as a function of list-length, but that the complex span-fluid abilities correlation remains constant across list-lengths from lists as short as two items. Furthermore, regression and factor analytic results suggested that the longest simple span list-lengths and all of the complex span list-lengths had both unique and shared variability in predicting fluid abilities, but that estimates of primary memory did not uniquely predict fluid abilities. It is suggested that complex spans, generally, predict higher-order cognition to a greater extent than do simple spans because complex spans require retrieval of items that have been displaced from primary memory due to the processing component of these tasks. Items in simple spans will also be displaced from primary memory but only after primary memory has become overloaded.