This research was aimed at the theoretical and experimental investigation of wetting behavior of immiscible droplets sitting on filaments and related applications in oil-water separation. This work consisted of three interrelated parts. Firstly, the engulfing behavior of two immiscible droplets sitting on a microfilament was studied theoretically; effects of the wetting properties and geometries of the droplet-on-filament system on the wetting morphology and capillary pressure were examined by detailed numerical simulations. Secondly, adhesion force and wetting area of a droplet bridge between two parallel plates were investigated via numerical simulation at varying contact angle and plate spacing. Finally, ultrathin continuous polymer nanofibers with very high hydrophobicity were produced by means of electrospinning technique. Experiments setup based on electrospun nanofiber membranes was demonstrated successfully for oil-water separation. The research results can be used to develop novel, low-cost, high-efficiency nanofibrous materials for oil-water separation and oil-spill sorption.