This is inter alia so because when known reserves start to be depleted, greater effort typically is dedicated to identifying new reserves as a replacement. Furthermore, the quality of statistics on proven reserves as published e.g. by British Petroleum is substantially affected by the mismatch between private information and public information, as private information held by companies and government officials involved in exploration is only partially divulged for strategic economic and political reasons. Statistical information on extraction (production) and use (consumption) of primary fuels and products is much more reliable.