A method of controlling fluid flow in a fluid network system by means of a plurality of fluid machines. The disclosure provides a simple empirical method of identifying network characteristics of the fluid network system used for providing the required fluid flow rate in the fluid network system utilizing minimal fluid machine power. The method includes the steps of determining a relation between a change in fluid machine speed and a corresponding change in fluid flow rate for each of the plurality of fluid machines empirically; determining a minimum total fluid machine power which provides a minimum required flow rate in the fluid network system based on a constraint involving the relation between the fluid flow rate and the corresponding fluid machine speed, and controlling a speed of the plurality of fluid machines such that the minimum total fluid machine power in the fluid network system is attained.