A dynamic method was used to determine the vapor pressures of perfluorooctanoic, -nonanoic, -decanoic, -undecanoic, and -dodecanoic acids. Measurements were made over the temperature range from (59.25 to 190.80) degrees C for perfluorooctanoic acid, from (99.63 to 203.12) degrees C for perfluorononanoic acid, from (129.56 to 218.88) degrees C for perfluorodecanoic acid, from (112.04 to 237.65) degrees C for perfluoroundecanoic acid, and from (127.58 to 247.36) degrees C for perfluorododecanoic acid. Pressures ranged from (0.128 to 96.50) kPa for perfluorooctanoic acid, from (1.12 to 99.97) kPa for perfluorononanoic acid, from (3.129 to 99. 97) kPa for perfluorodecanoic acid, from (0.616 to 99.97) kPa for perfluoroundecanoic acid, and from (0.856 to 99.96) kPa for perfluorododecanoic acid. A sealed vial experiment demonstrated that perfluorooctanoic acid sublimes at room temperature.