AlxGa1-xN samples covering the entire range of alloy compositions, 0≤x≤1, were grown by plasma-assisted MBE on c-plane sapphire substrates. The aluminum mole fraction was determined, by three different techniques, namely, x-ray diffraction, secondary ion mass spectroscopy, and Rutherford backscattering spectrometry. The energy bandgaps of the alloys were obtained from low temperature reflectance spectra. The data lead to a bowing parameter of b=1.0 eV in relating the bandgap of the AlxGa1-xN alloy to its chemical composition. A discussion of bowing parameter determination is presented along with possible causes for the large dispersion in previously reported bowing parameter values.