The hyperfine structure splitting and the isotope shift of the neutron-deficient gold isotopes 194−191Au in the optical transition 5 d 9 6 s 2 2 D 3 2 → 5 d 10 6 p 2 P 1 2 (627.8 nm) have been determined by collinear laser spectroscopy at the on-line isotope separator ISOLDE. The nuclear magnetic moments, spectroscopic quadrupole moments and changes in the mean square charge radii are deduced. Experimental electromagnetic moments and deformation parameters are compared with results of a particle-triaxial-rotor model calculation for both odd- A and odd-odd gold nuclei. Very good overall agreement between calculation and experimental data has been achieved. We find, for the first time, consistent evidence for a relatively large contribution from hexadecapole deformation ( ϵ 4 = 0.06, β 4 = −0.05) to odd- A gold isotopes ground states in the region of 183 ≤ A ≤ 197. Calculated values of quadrupole deformation are consistent with the prolate-to-oblate shape change between ground states of 186Au and 187Au. In addition, our results suggest another shape change between 190Au (oblate) and 191Au (triaxial). The former change is accompanied by a considerable change in quadrupole deformation, the latter occurs at almost constant deformation.