The wide use of examination scores for different educational purposes in society in the present le washback, a term commonly used to refer to the influence of language testing on teaching and learning, a distinct educational phenomenon (Cheng, 2004). The purpose of this study was to investigate the possible washback effects of the reading test, a component of the Diploma English test of Grade 12, in the Sultanate of Oman on teaching. The main aspects studied were: the relationship between the reading exam and the textbooks in terms of the sub-skills and question types being tested, teachers' perceptions and knowledge of the reading exam; and the washback effects of the reading exam on teachers' methodology of teaching reading. To address these issues, exam and textbooks analyses were conducted and qualitative and quantitative data analyses were conducted on the data obtained from surveying 83 teachers. Content analysis was conducted to interpret qualitative data elicited from interviews with five teachers. The study found that the reading exam has washback effects on many aspects related to teaching. Findings indicated positive washback of the exam since it assessed the same sub-skills and the question types represented in the textbooks. Questionnaire results found that the majority of the teachers expressed positive rather than negative perceptions about the exam. Most of the teachers appeared satisfied about recent exam changes and indicated a good range of awareness of the exam's outcomes and sub-skills and format. Interview findings showed an exam influence on the methodologies used by the teachers to teach reading (except for some techniques used including reading aloud, group and pair work and the use of glossaries and dictionaries). The findings of this study indicated extensive washback effects of the reading exam confirm the fact that exams can be used to establish reforms and innovations in the content and methodology of language teaching.