The intraocular expansion of perfluoromethane (CF4), perfluoroethane (C2F6), and perfluoropropane (C3F8) was determined by a direct method for measuring intravitreal gas. A bubble of CF4 was found to expand 1.9 times the volume initially injected; C2F6 expanded 3.3 times; C3F8 expanded four times. The expansion characteristics of the experimental gases were compared with those of sulfur hexafluoride (SF6) and octofluorocyclobutane (C4F8), two gases already in clinical use.