2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/131692We study invariant contact p-spheres on principal circle-bundles and solve the corresponding existence problem in dimension 3. Moreover, we show that contact p-spheres can only exist on (4n-1)-dimensional manifolds and we construct examples of contact p-spheres on such manifolds. We also consider relations between tautness and roundness, a regularity property concerning the Reeb vector fields of the contact forms in a contact p-sphere.23 pages, to appear in Annales de l'Institut Fourier, GrenobleGeometric TopologyDifferential Geometry53D10; 55R25; 58A15text