A description is given of the methods used to obtain precise values for the resonance energies and half-widths in proton capture reactions. A target chamber designed for this purpose is described. Proton capture in Al 27 has been investigated in the proton energy range 500 keV to 1400 keV. For all known resonances energy values are given. For some of the resonances the true half-widths and for the rest upper half-width limits are given.