Rod O'Donnell writes here that there is a wide and deep confusion in contemporary economics about the concept and role of opportunity cost (OC). O'Donnell states that his main grounds for making this claim are the muddled, variable, and sometimes conflicting treatments of OC in modern textbooks; the disturbing empirical results in surveys of both top economists and first-year students by Ferraro and Taylor (2005); and the unsatisfactory nature of most of the responses to the FT paper in published and unpublished discussion. O'Donnell states that he and Parkin are in broad agreement that confusion exists to a significant degree, that this is important for mainstream economics, and that it merits resolution. O'Donnell however finds himself unsatisfied with Parkin's diagnosis and cure and so offers a response which, while fully agreeing with the need for reexamination, is critical in relation to Parkin's contribution. O'Donnell restricts himself in this article to general, conceptual issues and to clarifications of some complexities.