Hadronic events produced in e+e- collisions by the LEP collider and
recorded by the OPAL detector were used to form distributions based on the
number of reconstructed jets. The data were collected between 1995 and
2000 and correspond to energies of 91 GeV, 130-136 GeV and 161-209 GeV.
The jet rates were determined using four different jet-finding algorithms
(Cone, JADE, Durham and Cambridge). The differential two-jet rate and the
average jet rate with the Durham and Cambridge algorithms were used to
measure alpha_s in the LEP energy range by fitting an expression in which
O(alpha_s^2) calculations were matched to a NLLA prediction and fitted to
the data.  Combining the measurements at different centre-of-mass
energies, the value of alpha_s(M_Z)  was determined to be
         
alpha_s(M_Z)  = 
0.1177 +- 0.0006 (stat.) +- 0.0012 (expt.) +- 0.0010 (had.) +- 0.0032 (theo.).