Abstract: The proved reserve definition given by Securities and Exchange Commission (SEC) is an essential basis for reservcs appraisals of all joinl-stock oil companies. but it can be rcgarded as a special case of the reserves classification defined by SPE. ln-depth understanding of SPE's definition, particularly, of relationship among proved, probable and possible reserves (PPPR) is favorable for right understanding of SEC's proved reserve definition. The correlation of SPE reserves is generally divided into three types; PPPR occurs 1) only in different blocks or reser-voirs; 2) in the sarne oil-gas reservoir, and 3) in accordance with original oil in-place (O0IP).

Key words: reserve, classification, apprasal, proved reserve, probable reserve