A simple oil/water/surfactant model is used to study self-​assembly of surfactants. The model contains only the most obvious elements: oil and water do not mix; a surfactant is an amphiphilic mol. with one side hydrophilic and the other hydrophobic. Computer simulations reveal surprisingly rich structural detail. Micelles form spontaneously in the water phase with a surfactant monolayer at the interface. Depending on head-​group shape, disk-​like or spherical micelles form at a particular surfactant concn. The simulations yield a complete micellar size distribution function. Dynamic processes of surfactant entry and exit from micelles and of micelle fusion or breakdown are observed.