discoveries--has been declining recently. Consumption has been rising 

 faster than discoveries. In 1975 (the latest information available) oil 

 reserves declined by about 5 percent, and natural gas reserves declined 

 nearly 4 percent. 



Figure 1. Petroleum resource terms and classification 

 system (Source: References), 



IDENTTIRED 



Demonstrated 



Measured 



Indicated 



Inferred 



UNDISCOVERED 



o 



LU 



RESERVES 



RESOUllt-ilf'"- 



■ncreasing degree of geologic assurance 



1. Resources - naturally occurring materials 

 concentrated so that economic extraction is 

 potentially feasible. 



2. Reserves - that portion of resources which are 

 presently economically extractable. 



3. Undiscovered recoverable resources - those 

 economic resources yet undiscovered which are 

 estimated to exist in favorable geologic 

 environments. 



