A description this effort was focused on determining the effectiveness of ozone z and chlorine dioxide d in the bleaching of pulp as compared to various control sequences containing a first stage using chlorine dioxide without ozone more specifically to demonstrate that the clo 2 to o 3 ratio in d z in the first stage of a bleaching sequence is important to the preservation of strength of the final paper elaborated from bleached pulp the methods of the invention are applicable to all bleachable pulps including kraft sulphite oxygen delignified chemical mechanical and chemical mechanical pulps most preferably the methods of the invention are applicable to low consistency cellulose pulps consistency less than or equal to about 5 percent the ratio of chlorine dioxide to ozone in the d z stage which will accomplish the desired strength characteristics substantially equivalent to the control sequence preferably ranges from about 0 5 to about 2 5 more preferably from about 0 8 to about 1 5 the ratio of chlorine dioxide to ozone in the z d stage which will accomplish the desired strength characteristics substantially equivalent to the control sequence also preferably ranges from about 0 5 to about 2 5 more preferably from about 0 8 to about 1 5 in bleaching sequences of the invention the temperature of d z and z d stages typically and preferably ranges.