The lifetime of the 6s6p P11 state of mercury has been determined by the zero-field level-crossing technique (Hanle effect) to be τ=(1.31±0.08)×10-9 sec. This result yields a value of f=1.18 for the oscillator strength of the 1850- line. From this lifetime result and other experimental data we have calculated the intermediate coupling coefficients for the mixing of the 6s6p P13 and P11 states by three different methods. All three methods are in good agreement. © 1965 The American Physical Society.