Cita APA (7a ed.)

Rühl, W. (1982). Tar (extra heavy oils) sands and oil shales. Ferdinand Enke.

Cita Chicago Style (17a ed.)

Rühl, Walter. Tar (extra Heavy Oils) Sands and Oil Shales. Stuttgart: Ferdinand Enke, 1982.

Cita MLA (9a ed.)

Rühl, Walter. Tar (extra Heavy Oils) Sands and Oil Shales. Ferdinand Enke, 1982.