A fluid discrimination system can include a fluid discriminator which selects through which of multiple outlet flow paths a fluid composition flows, the selection being based on a direction of flow of the fluid composition through the discriminator, and the direction being dependent on a fluid type in the fluid composition. Another fluid discriminator can include a structure which displaces in response to a fluid composition flow, whereby an outlet flow path of the fluid composition changes in response to a change in a ratio of fluids in the fluid composition. A method of discriminating between fluids can include providing a fluid discriminator which selects through which of multiple outlet flow paths a fluid composition flows in the well, the selection being based on a direction of flow of the fluid composition through the discriminator, and the direction being dependent on a ratio of the fluids in the fluid composition.