We fabricated epitaxial Mg-Al-O(001) tunnel barriers using direct/indirect plasma oxidation and natural oxidation of an MgAl layer for use in Fe/Mg-Al-O/Fe magnetic tunnel junctions. All the oxidation processes formed epitaxial Mg-Al-O barriers, and a wide resistance area (RA) product range (10(1) - 10(6) Omega.mu m(2)) and large tunnel magnetoresistance (TMR) ratios (185%-212%) at room temperature were achieved by optimizing the MgAl thickness (t(MgAl)). Near optimum oxidation conditions and tMgAl, small bias voltage dependence of the TMR ratio, and distinct local minima in the dI/dV spectra for the parallel magnetic configuration were observed, indicating that coherent tunneling transport was significant. This study showed that Mg-Al-O coherent tunnel barriers have excellent formability in a wide RA product range. (C) 2014 AIP Publishing LLC.