Measurements of inclusive semileptonic branching                               
fractions of b hadrons in Z0 decays                                            
  
Measurements of the semileptonic branching fractions of                        
inclusive b hadrons, BR(b --> l) and BR(b --> c --> l), are                    
obtained using 3.6 million multihadronic Z0 decays collected                   
with the OPAL detector. An enriched Z0 to bb sample is obtained                
with a lifetime flavour-tagging technique. Selected leptons                    
from this sample are then classified according to their                        
origin, which is determined by comparing the distribution                      
of several kinematic variables using artificial neural networks.               
Combining the results for electrons and muons, the                             
BR(b --> l) result is the most precise measurement to date at                  
the Z0 resonance. Agreement between data and various                           
semileptonic decay lepton spectra and fragmentation functions                  
is also investigated.                                                          
  
 Parallel session :7                   
 Plenary  session :3