World Prison Population List, King's College International Centre for Prison Studies, June 27, 2005. Excerpt:
Over 9 million people are held in penal institutions throughout the world, mostly as pre-trial detainees (remand prisoners) or having been convicted and sentenced. Almost half of these are in the United States (2.09m), China (1.55m plus pretrial detainees and prisoners in 'administrative detention') or Russia (0.76m).
Read the full text of the report here [PDF]. Reported in JURIST's Paper Chase here.