Between 1987 and 1997, considerable research effort has been devoted to improving the efficiency of solar thermal power plants with distributed collectors, not only in the field of optical technology but also from the control and optimisation viewpoint. The article deals with this second aspect, and presents results obtained in the control of the distributed solar collector field of the solar power plant of Almeria (Spain) using a fuzzy logic control approach. A distributed collector field consists of a series of parabolic mirrors which reflect solar radiation onto a pipe where oil gets heated while circulating. The object of the control system is to maintain the outlet oil temperature of the field (collector field) at a desired level in spite of disturbances such as changes in the solar radiation level, mirror reflectivity or inlet oil temperature. Since solar radiation cannot be adjusted this can only be achieved by adjusting the flow of oil. An incremental fuzzy PI controller (IFPIC) has been developed to cope with this control problem in which all parameters of a PI controller are updated online as a function of the operating conditions of the controlled plant, thus improving the behaviour of the classical fixed PI controllers which are usually employed. The strategy has been implemented in series with a simple feedforward controller which compensates for the disturbances acting on the system. Simulation results using a nonlinear computer model of the field and real tests are provided.