In order to maintain or improve a jurisdiction's energy security, its energy system needs to meet the demands of its energy services with affordable and preferably environmentally acceptable flows of energy. Since diversity can be a factor in the long-term survival of a system, having a diversity of energy flows is frequently treated as a proxy for energy security. This paper examines the relationship between energy security and the diversity of an energy system's energy flows using a set of energy security indicators and the Shannon-Wiener diversity index. Although diversity may be considered necessary for maintaining and improving energy security, the quantitative analysis of the relationship shows that an energy flow considered diverse need not be secure and that a secure energy flow need not be considered diverse. Examples of this relationship are included. These findings can prove useful to policy makers and energy analysts when developing transition strategies for a jurisdiction's energy system. (C) 2014 Elsevier Ltd. All rights reserved.