This white paper gives an overview of the proposed Gemini/Subaru Wide-Field Multi-Object Spectrograph (WFMOS) and the proposed redshift surveys of 2.6 million galaxies with 0.5<z<3.3 over 2000 deg^2 of sky. These surveys will probe the baryonic acoustic oscillations in the galaxy power spectrum with unprecedented precision and over a range of redshifts and deliver dark energy w(z) constraints an order of magnitude better than current limits. We discuss the requirements on precursor observations and on calibrations, the systematics in the method and the quantitative precision obtainaible in distance-redshift and expansion-rate-redshift measurements which feed in to the w(z) precision. We also outline the technological and scientific strengths and risks which might be associated with the project and the relationship of WFMOS to other baryon oscillation experiments.