To date, experimental comparisons of menu layouts have concentrated on variants of hierarchical structures of sequentially presented menus. Simultaneous menus - layouts which present multiple active menus on a screen at the same time - are an alternative arrangement that may be useful in many web design situations. This paper describes an experiment involving a between-subject comparison of simultaneous menu and their traditional sequential counterparts. Twenty experienced web users used either simultaneous or sequential menus in a standard web browser to answer questions based on US Census data. For novice users performing simple tasks the simplicity of sequential menus appears to be helpful, but for most tasks and most users there is good evidence to believe that simultaneous menus speed performance and improve satisfaction. Design improvements can amplify the benefits of simultaneous menu layouts. (Also cross-referenced asUMIACS-TR-99-60)