Diffusion couple experiments were carried out with San Carlos olivine (Fo 90 ) and NiFe alloys (Ni 100 , Ni 97 Fe 3 , Ni 90 Fe 10 ) or other olivine compositions (Fo 100 , Fo 25 ) in order to determine the dependence on temperature, oxygen fugacity, composition and crystallographic orientation of Ni diffusion coefficient (D Ni ) in olivine. Experiments at 1 atmosphere total pressure cover a temperature range of 900–1445°C with run durations from 48 to 2155 h at different oxygen fugacities. In an Arrhenius plot the best fit for all data for Fo 90 yields an activation energy (E D ) of 220 ± 14 kJ/mol and an fO 2 dependence of (1/4.25)·Δ log fO 2 = Δ log D Ni . The relationship between diffusion coefficients along different crystallographic axes at 1200°C is given by D [001] ≈ 6·D [100] ≈ 6·D [010] . D Ni depends strongly on the major element (i.e. Fe/Mg) composition of olivine and decreases by about 1 order of magnitude as the olivine composition changes from Fo 35 to Fo 90 . Thus, experimental investigations in Fe-free systems cannot be applied to natural samples. For calculation of residence times or cooling rates the present Ni data yield shorter timescales compared to those obtained using diffusion data published until now. In addition to Ni diffusion coefficients, Fe-Mg, Mn and Ca diffusion data were obtained from some of the same diffusion couples (Fo 90 -Fo 100 ). It is found that the activation energies, E D [Ni] ≅ E D [Fe-Mg] ≅ E D [Mn] ≤ E D [Ca]. All diffusion coefficients are strongly dependent on the major element composition of olivine.