The rate constants for the gas-phase reactions of phenanthrene, phenanthrene-d(10), and 1-, 2-, 3-, and 9-methylphenanthrenes with the hydroxyl radical were measured using the relative rate technique over the temperature range of 323-403 K and at a total pressure of 760 Torr. On-line mass spectrometry was used to monitor the concentrations of reactants as a function of time. The following Arrhenius expressions have been determined for these reactions (in units of cubic centimeters per molecule per second): (6.46(-1.39)(+1.77)) x 10(-12) exp[(477 +/- 89)/T] for phenanthrene, (3.38(-1.91)(+4.42)) x 10(-12) ex [(745 +/- 301)/T] for phenanthrene-d(10), (0.246(-0.115)(+0.218))x 10(-12) exp[(1420 +/- 242)/T] for 1-methylphenanthrene, (2.54(-1.49)(+3.57)) x 10(-12) exp[(964 +/- 322)/T] for 2-methylphenanthrene, (2.97(-0.56)(+0.69)) x 10(-12) exp[(926 +/- 77)/T] for 3-methylphenanthrene, and (7.75(-5.02)(+14.3)) x 10(-12) exp[(679 +/- 372)/T] for 9-methylphenanthrene. The Arrhenius parameters determined here for phenanthrene-djo and 1-, 2-, 3-, and 9-methylphenanthrene are the first to be reported.