Energy spectra were obtained experimentally for fission fragments escaping from backed films of enriched uranium dioxide that were less than 11 µm thick. The data were reduced to give values for the relative average escape energies (R), escape fractions (S) and energy deposition efficiencies (D). A mathematical model was developed to synthesize these results using a Monte-Carlo-type computer code. This code included the fission-fragment masses, yields, and initial energies, the experimental source-detector geometry, a range-energy relationship, an energy-loss relationship and a function for the pulse-height defect in surface-barrier detectors. Various functions for these last three parameters were used in combination to obtain results that duplicated the experimental spectra and R, S and D values. The agreement was obtained with range proportional to (energy)1/2, the square energy-loss function, and pulse-height defect = A (E) (M-B), where A and B are constants and E and M are energy and mass, respectively. The experimental detection functions were removed from the code, and the spectra and R, S and D values were calculated for a 2π geometry. These values agreed well with those calculated using weighted averages for range and initial energy.