The YBa₂Cu₃O_6+x structures have been fluorinated by a gas phase exchange technique, and 19F NMR was used to identify the structural fluorine. Magnetic susceptibility measurements showed that the fluorination turned a marginally nonsuperconducting sample into a 40 K superconductor, as well as that it raised the onset of the superconducting transition of the 60 K superconductor YBaCuO6.7 to about 100 K.