We report constraints on antineutrino oscillation parameters that were obtained by using the two MINOS detectors to measure the 7% muon antineutrino component of the NuMI neutrino beam. In the Far Detector, we select 130 events in the charged-current muon antineutrino sample, compared to a prediction of 136.4±11.7(stat)-8.9+10.2(syst) events under the assumption |Δm̅ 2|=2.32×10-3  eV2, sin⁡2(2θ̅ )=1.0. Assuming no oscillations occur at the Near Detector baseline, a fit to the two-flavor oscillation approximation constrains |Δm̅ 2|<3.37×10-3  eV2 at the 90% confidence level with sin⁡2(2θ̅ )=1.0.