A flexible RO (FLERO) membrane desalination configuration employing a pressure intensifier and partial concentrate recycle was investigated with respect to operational flexibility and specific energy consumption (SEC). Decomposition of FLERO configuration and its operation into a membrane processing and concentrate recycle units allows fluid flow regulation at low pressure and adjustable product water recovery. Operational analysis, along with experimental evaluation using a small-scale spiral wound system, demonstrated a desalting capability over a wide range of both permeate recovery and source water salinity. Moreover, in the FLERO configuration a relatively low-pressure pump can be used, even for seawater desalination. However, the SEC for the FLERO configuration is higher, at the same recovery and permeate productivity, relative to conventional single-pass with energy recovery. Nonetheless, given its operational flexibility, in terms of handling both a wide range of source water salinity and recovery and source water salinity and need for low-pressure RO water feed pump. Given the above, FLERO should be ideal for small-scale applications, particularly in remote locations, and field evaluation is warranted to establish its long-term benefits. Large-scale FLERO applications would depend on the availability of suitable energy recovery devices of sufficient efficiency for large desalination capacity.