Oxygen has always been an attractive oxidant for the pulp and paper industry due to it being cheap and harmless for the environment. However, it has lower lignin-cellulose selectivity, therefore the degree of delignification achieved at the oxygen stage is ultimately limited by its industrial pulp strength - 45-50%. In this study, to enhance the degree of delignification, the addition of sodium perborate and hydrogen peroxide at the oxygen stage was examined. At the same active oxygen (approximately 0.5%) content, the degree of delignification increased from 45.56% to 49.42% using hydrogen peroxide and to 52.96% with sodium perborate. For the same selectivity parameter with control, the delignification degree can be increased to 57.59% with the addition of sodium perborate, which includes 1% active oxygen. Moreover, the costs of using sodium perborate and hydrogen peroxide were compared with respect to commercial employability. It was determined that the use of sodium perborate was more effective than that of hydrogen peroxide for delignification of the oxygen stage.