The use of supplemental oxygen by emergency nurses has important implications for patient outcomes, yet there is significant variability in oxygen administration practises. Specific education related to oxygen administration increases factual knowledge in this domain; however, the impact of knowledge acquisition on nurses' clinical decisions is poorly understood. This study aimed to examine the effect of educational preparation on 20 emergency nurses' decisions regarding the assessment of oxygenation and the use of supplemental oxygen. A pre-test/post-test, quasi-experimental design was used. The intervention was a written, self-directed learning package. The major effects of the completion of the learning package included no change in the number or types of parameters used by nurses to assess oxygenation, a significant decrease in the selection of simple masks, a significant increase in the selection of air entrainment masks, fewer hypothetical outcomes of unresolved respiratory distress and more hypothetical outcomes of decreased respiratory distress. As many nursing education programs are aimed at increasing factual knowledge, while experience remains relatively constant, a greater understanding of the relationship between factual knowledge and clinical decisions is needed if educational interventions are to improve patient outcomes.