Steady-state and pulsed methods have been applied to static phosphorescence and fluorescence quenching for phenanthrene caused by oxygen and nitric oxide. The characteristic fluorescence quenching distances have been determined for oxygen (8.70.5 ) and nitric oxide (8.90,5 ); the phosphorescence quenching involves an exchange mechanism, and measurements have been made on the characteristic quenching distances R0 and exchange-interaction attenuation parameters L. Estimates have been made on the rate constants for dynamic quenching of the triplet excited states of phenanthrene in low-viscosity liquids, which agree well with the measured values for hexane.