A simple technique to generate in-plane forming limit curves has been developed. This technique is based on the Marciniak biaxial stretch test using a single punch/die configuration, but the specimen and washer geometries have been modified in order to achieve failure in both drawing and stretching deformation modes. The experimental technique is described, and the advantages of using this inplane method over the conventional out-of-plane dome method are discussed. It is shown that (a) sheet thickness has an intrinsic influence on forming limits that is not related to small bending strain variations with thickness or to deformation in the presence of friction and curvature, (b) plastic anisotropy (t= value) does not substantially affect forming limits, and (c) in-plane forming limits are slightly lower (5 to 6 pct) than out-of-plane forming limits near plane strain;​ these differences are smaller than previously reported values (12 to 15 pct) in the literature.