There is significant uncertainty in these estimates due to the illicit and clandestine nature of the various drugs and the limited data currently collected. The estimate of 260 to 270 pure metric tons of cocaine was determined through the integration of many routinely reported sources such as the potential cocaine production estimates reported annually by the Central Intelligence Agency, the Office of National Drug Control Policy’s annual consumption estimate, and worldwide seizure statistics. The estimate of 13 to 18 pure metric tons of heroin was based on the number of users, their frequency of use and expenditures, and the retail price of heroin. Domestic production is the primary source of methamphetamine available for domestic demand. The largest component of the 110 to 140 pure metric tons of methamphetamine is manufactured from diverted Canadian and United States pseudoephedrine and ephedrine. The 10,000 to 24,000 metric ton estimate of marijuana availability was based on a two-part methodology that separately derived the quantities of foreign and domestically produced marijuana available. The speculative estimate of domestic marijuana production was calculated by applying three hypothetical seizure rates to domestic cannabis eradication figures. Based upon the current estimates’ uncertainties, the most important action items in improved drug availability estimates should relate to domestic marijuana cultivation, a more accurate signature of heroin production, consumption habits of heroin users, and trafficking flow patterns through Mexico and Canada. It is important that policymakers and Congress fund additional data collection systems to make any real progress in developing reliable estimates that will contribute to reasoned shifts in policy and strategy. 12 figures, 59 tables, 17 appendices, 17 references