·          Student Aid; Argonne National Laboratory; Argonne, IL; Summers 1959, 1960, 1961.

·          Process Design Engineer; American Oil Company; Whiting, IN; Summer 1962.

·          Power Plant Engineer; Linde Gas Division of Union Carbide; East Chicago, IN; Summer 1963.

·          Teaching Assistant; Department of Chemical Engineering; Univ. of California; Berkeley; 1962-64; 1966-67.

·          Research Assistant; Department of Chemical Engineering; Univ. of California; Berkeley;  1964-66.

·          Assistant Professor; Department of Chemical Engineering; Univ. of Colorado; Boulder; January 1968-73.

·          Consultant; Dow Chemical Company; Midland, Michigan; 1969-71.

·          Fulbright-Hayes Lecturer; Dept. of Chem. Eng.; Istanbul Technical Univ.;  Turkey; 1974-1975.

·          NSF-NATO Senior Fellow in Science; Fluid Mechanics Research Institute; University of Essex; Colchester, England; June-August, 1975.

·          Consultant; Laramie Energy Technology Center; DOE; Laramie, WY; 1976-77, 1979-81.

·          Program Director; Thermodynamics and Mass Transfer Program; NSF; Washington, DC; 1977-1978.

·          Associate Professor; Department of Chemical Engineering; Univ. of Colorado; Boulder; 1974-79.

·          Consultant; National Bureau of Standards; Department of Commerce; Boulder, CO; 1979-80.

·          Professor; Department of Chemical Engineering; Univ. of Colorado; Boulder; 1979 to date.

·          Fulbright-Hayes Senior Research Fellow; Institut für Eisenhüttenkunde; Aachen Technical University; Aachen, West Germany; 1981-1982.

·          Consultant; Martin Marietta Corporation; Denver, Colorado; 1982.

·          Research Affiliate; Institute of Arctic and Alpine Research; Univ. of Colorado; Boulder; 1984-91.

·          Visiting Keating-Crawford Professor; Dept. of Chem. Eng.; Univ. of Notre Dame; South Bend, IN; Fall, 1985.

·          Research Fellow; Center for Low-Gravity Fluid Mechanics and Transport Phenomena; Univ. of Colorado; Boulder; 1986-92; Co-Director, 1989-90.

·          Manager for Space-Made Films, Membranes, & Liquid Membranes, Bioserve Space Technologies Center; Univ. of Colorado; Boulder; 1987-92.

·          Co-Director of the NSF Industry/University Cooperative Research Center for Separations Using Thin Films; Univ. of Colorado; 1988-99.

·          Guggenheim Fellow and Fulbright Research Fellow; Mathematical Inst., Oxford Univ; Oxford, UK; 1988- 1989.

·          Guggenheim Fellow; Dept. of Chem. Eng.; Indian Inst. of Science; Bangalore, India; Summer, 1989.

·          Consultant; Bend Research, Inc.; Bend, Oregon; 1990-93.

·          President's Teaching Scholar; University of Colorado; 1990 to date.

·          Research Fellow; Institute of Arctic and Alpine Research; Univ. of Colorado; Boulder; 1991-99.

·          Director, NSF Research Experiences for Undergraduates Summer Site Program, University of Colorado; 1993-2000.

·          Visiting Professor; Center for Membrane Science & Tech.; Univ. of Twente; Enschede, Netherlands; 1995-96.

·          NSF GOALI Faculty Fellow; Chevron Research and Technology; Richmond, California; 1996.

·          NSF GOALI Faculty Fellow; 3M Corporate Research and Technology; St. Paul, Minnesota; 1996.

·          Consultant, 3M Company, St. Paul, Minnesota, 1998-99.

·          Visiting Research Fellow; Research School of Chemistry; Australian National Univ.; Canberra, ACT, Australia; 2003.

·          Rieveschl Ohio Eminent Scholar of Membrane Technology and Professor Emeritus; Univ. of Cincinnati; Cincinnati, OH; 2000-2005.

·          Co-Director, NSF Industry/University Cooperative Research Center for Membrane Applied Science and Technology; Univ. of Cincinnati; 2000-2005.

·          Director, NSF Research Experiences for Undergraduates Summer Site Program, Univ. of Cincinnati; 2001-2005.

·          Director, NSF Integrative Graduate Research Education and Training Program, Univ. of Cincinnati; 2003-2005.

·          Isaac M. Meyer Chair Professor, Dept. of Chemical & Biomolecular Engineering, National Univ. of Singapore; 2005-2008.