The folds of Osage County, Oklahoma, consist primarily of low domes, shallow basins, terraces, and inverted terraces. Two of the more important theories concerning the origin of these folds are (1) settling over buried hills and (2) horizontal movement along buried fault planes. The chief objections to the first theory are (a) the thickness and character of the sediments, (b) the persistence of the folds through numerous unconformities, and (c) the great number of both domes and basins, and the similarity between them. A vital objection to the second theory is that horizontal movement along buried fault planes would result in folds more elongate than those formed in Osage County. The characteristics of these folds, especially their domal form, experimental results, and th oretical considerations, all indicate that they are primarily the result of compressive forces acting more or less equally in all directions, although other factors may have exerted a modifying influence.