توثيق جمعية علم النفس الأمريكية APA (الطبعة السابعة)

Leffler, G. L. (1949). Average prices of gas, water and electric light and power companies in Pennsylvania since 1939.

توثيق أسلوب شيكاغو (الطبعة السابعة عشر)

Leffler, George Leland. Average Prices of Gas, Water and Electric Light and Power Companies in Pennsylvania Since 1939. State College, Pa, 1949.

توثيق جمعية اللغة المعاصرة MLA (الطبعة الثامنة)

Leffler, George Leland. Average Prices of Gas, Water and Electric Light and Power Companies in Pennsylvania Since 1939. 1949.