Many industrial applications of computer vision require fast, accurate, classification and orientation of known objects. For those objects which exhibit circular markings or circular surfaces, it is possible to determine object orientation from a single visual image. In this paper, a technique is presented which uses the parameters of an ellipse fit to points in the image to specify the orientation of the corresponding circular object surface. Location of candidate ellipse points in the image is accomplished by exploiting knowledge about object boundaries and image intensity gradients. A second order ellipse equation is fit to the candidate points using a nonlinear error measure based on the equation of a general conic and an average gradient constraint. The technique presented is applied to the task of estimating the orientation of a discrete transistor against a uniform background, and results are summarized for 138 images.