Calculations of the microcanonical isomerization rates for vibrationally excited ketene are presented. The calculations utilize the quantum reactive scattering methodology of absorbing boundary conditions with a discrete variable representation to obtain the cumulative reaction probability for one form of ketene to isomerize via the oxirene intermediate, and were carried out with model 1-, 2-, and 3-degree-of-freedom potential energy surfaces constructed using ab initio data. Significant differences are seen in the energy dependent features of the microcanonical rate for the single mode and multi-mode potentials; e.g., the single mode potential exhibits tunneling resonances with widths of around 1 cm(-1), while the calculations involving more than one degree of freedom have additional resonant features that have widths around 10 cm(-1) and also exhibit non-Breit-Wigner resonant line shapes. This suggests that many of the resonance features are best described as Feshbach (energy transfer, or dynamical) resonances that result because of a strongly bent region on the multi-mode potential energy surfaces. The calculated rates show reasonable qualitative agreement with the experimental results of Lovejoy and Moore [J. Chem, Phys. 98, 7846 (1993)].