Examples are given of the application of computer code FUELCYC to fuel cycle analysis of pressurized water, organic moderated, and heavy water reactors. Properties of these reactors evaluated include the flux energy spectrum, changes in fuel composition and effective cross sections on irradiation, and changes in power density distribution. The effects of different initial fuel enrichments and six different fuel and poison management procedures on the average burnup of fuel, its maximum burnup, the peak-to-average power density ratio and fuel cycle costs are investigated. Fuel cycle costs may be reduced by having good neutron economy, high burnup, and a steady fueling procedure in which neutrons are not wasted in control poison. Of the fueling methods examined, out-in fueling, or some discontinuous approximation to it, seems best because of its flat power-density distribution and relatively low fuel cycle cost. Where mechanically feasible, bidirectional axial fueling is also advantageous because of the uniform fuel burnup it makes possible and its low fuel cycle cost.