Intentional discharges of oily ballast and bilge water is such a com- 

 mon practice that it is a greater source of oil pollution than oil spills. 

 Approximately 70 percent of all oil released from tankers is due to these 

 routine discharges [170], (See Figure 51.) After delivering oil, tankers 



Figure 51. Relative magnitude of oil influx from various tanker sources 

 (Source: Reference 169). 



100 



80 



UJ 

 C(0 



60 



40 



C-3 



70 



TANK 

 CLEANING 



CASUALTIES DISCHARGES TERMINALS 



must take on ballast water for the return leg of their voyage in order to 

 maintain seaworthiness. Oil clinging to storage tank walls is washed off 



190 



