The phenomenon of micrometre-sized objects moving autonomously in water has been of great interest. Because of their autonomous movement, these objects have more degrees of freedom of motion than that of an object moving on a water surface or at the bottom of a container. The mechanism of the autonomous motion sustained in an aqueous system of low Reynolds number has drawn much attention. Among the self-propelled objects, we have focused on micrometre-sized oil droplets in an aqueous surfactant solution. In this chapter, we review preceding studies on the self-propelled oil droplets from the standpoint of molecular designs where the self-propelled motion of the micrometre-sized oil droplets is controlled through the oil droplet-environment interaction. We further discuss the results obtained from the self-propelled oil droplets along with theoretical considerations. We believe that the current findings contribute to the potential applications of self-propelled oil droplets as carriers and/or probes in water for exploring and remediating environmental or biological systems in the future.