Monte Carlo simulations have been performed for catenanes composed of coarse-grained poly(ethylene oxide) in the melt. Simulations have also been performed for melts of single rings, in which the ring has a mass that is the sum of the masses of the two rings in a catenane. The numerical results from the simulations are compared with the predictions of an analytical expression derived for a very simple model of the catenanes. The simple model provides a rough approximation to the average asymmetries of the conformations, but it substantially underestimates the sizes. The internal motions of the catenanes are dominated by the movement of a bead relative to the center of mass of the other ring in the catenane.