INTRODUCTION: This study aims to investigate the use of oxytocin augmentation during labor in nulliparous women following Zhang’s guideline or the WHO partograph. MATERIAL AND METHODS: This is a secondary analysis of a cluster randomized controlled trial in 14 birth-care units in Norway, randomly assigned to either the intervention group, which followed Zhang’s guideline, or to the control group, which followed the WHO partograph, for labor progression. The participants were nulliparous women who had a singleton full-term fetus in a cephalic presentation and spontaneous onset of labor, denoted as group 1 in the Ten Group Classification System. RESULTS: Between December 2014 and January 2017, 7277 participants were included. A total of 3219 women (44%) received augmentation with oxytocin during labor. Oxytocin was used in 1658 (42%) women in the Zhang group compared with 1561 (47%) women in the WHO group. The adjusted relative risk for augmentation with oxytocin was 0.98 (95% CI 0.84-1.15; P = .8) in the Zhang vs WHO group, with an adjusted risk difference of -0.8% (95% CI -7.8 to 6.1). The participants in the Zhang group were less likely to be augmented with oxytocin before reaching 6 cm of cervical dilatation (24%) compared with participants in the WHO group (28%), with an adjusted relative risk of 0.84 (95% CI 0.75-0.94; P = .003). Oxytocin was administered for almost 20 min longer in the Zhang group than in the WHO group, with an adjusted mean difference of 17.9 min (95% CI 2.7-33.1; P = .021). In addition, 19% of the women in the Zhang group and 23% in the WHO group received augmentation with oxytocin without being diagnosed with labor dystocia. CONCLUSIONS: Although no significant difference in the proportion of oxytocin augmentation was observed between the 2 study groups, there were differences in how oxytocin was used. Women in the Zhang group were less likely to receive oxytocin augmentation before 6 cm of cervical dilatation. The duration of augmentation with oxytocin was longer in the Zhang group than in the WHO group.