Ruhl, Walter. <br/><br/>
Tar (Extra heavy oil) sands and oil shales  / 
by Walter Ruhl. 
 - Stuttgart:  Ferdinand Enke,  1982. 
 - 149p.;  23 cm. 
<br/><br/> Includes bibliographical references and indexes. 
<br/><br/><label>ISBN: </label>343292531X 
<br/><br/><label>Subjects--Topical Terms: </label><br/> Petroleum--Geology.<br/> Oil sands.<br/> Oil--shales.