1. Gas facts;American Gas Association,1967
2. Area measurement reports, various years (U.S. Department of Commerce, Washington, DC).
3. Managerial discretion and expense preference behavior;Awh;Review of Economics and Statistics,1985
4. Competition and monopoly in public utility industries;Behling,1938
5. The electric side of combination gas-electric utilities;Brandon;Bell Journal of Economics and Management Science,1971