The recovery of water during inland desalination processes using reverse osmosis, or RO, is often limited by the solubility of calcium sulfate, or CaSO4. Reducing or eliminating the presence of sulfate from the feedwater will allow the process to be operated at higher recoveries and produce less waste brine. Ion exchange may be used as a pretreatment method for the control and removal of sulfate using a hybrid ion exchange-reverse osmosis (HIX-RO) process. However, for viable application, it is imperative that the process is self-regenerating; that is, the use of external regenerants has to be avoided altogether. Various properties of the ion-exchange resin control the overall selectivity toward sulfate including the resin matrix and basicity of the functional group. Finer control over selectivity is also possible through mixing of characteristically different ion exchange resins. This study focused on how mixing anion exchange resins with different matrix and functional groups may optimize sulfate/chloride selectivity avoiding precipitation of CaSO4 for a specific brackish water. Finally, lab-scale results from an HIX-RO system are presented demonstrating higher RO recovery with no need for an external regenerant.