The effect of polysulfide (PS) and anthraquinone (AQ)addition on kraft cooking is investigated together with oxygendelignification of the high-yield PS/AQ kraft pulps. Additionof polysulfide and AQ increases pulp yield. The yield benefitis considerably lowered when cooking to kappa numbersbelow 27-28. Oxygen delignification to about 55%delignification preserves the yield increase attained by PS/AQaddition. For two-stage extended oxygen delignificationbeyond 55% kappa decrease , the yield increase is lowered.Peroxyacetic acid “activation” of the pulp followed by asecond oxygen stage also lowered the yield significantly.From the data presented, optimal yield for bleached pulpwould be reached when cooking with PS/AQ addition tokappa numbers between 40 and 45, followed by oxygendelignification to kappa numbers around 22. This could thenbe followed by bleaching with more selective bleachingchemicals like ozone and/or chlorine dioxide.