The PhD degree requirements include a minimum of 14 quarter-courses beyond the BS degree, six of which must satisfy distribution requirements in chemical and biological engineering and other departments. These may be waived for students entering with an MS degree and appropriate course background; however, students who enter with an MS degree must take a minimum of eight courses at Northwestern. Students working toward a PhD degree are expected to maintain a high standard of achievement in their academic programs. Permission to continue for a PhD after the first calendar year of study is granted based on review by the faculty of a student's academic achievement and progress in initiating research. Research progress is reviewed annually, beginning at the end of the second year. The qualifying exam consists of an oral defense of a written research proposal in which the student must demonstrate creativity, initiative, and a high level of professional ability. Final requirements for the degree include the presentation of a departmental seminar as well as completion and defense of a satisfactory PhD thesis in a timely manner. Students entering with a BS degree in chemical engineering take the qualifying exam by the ninth quarter of residence and usually complete the PhD in 4 ½ to 5 ½ years. Students entering with an MS degree in chemical engineering take the qualifying exam by the sixth quarter of residence and typically complete the PhD in 3 ½ to 4 ¼ years.