The preparation of the month end gold production report is required by the mine owners to regularly assess the performance of the plant against budgeted values. However the preparation of a gold production report is often complicated by the large inventory of gold in the carbon in pulp (CIP) or carbon in leach (CIL) tanks used to adsorb leached gold from the solution. Indeed a 600 m(3) CIP/CIL loaded with 15 g/L of activated coal charged with 8000 g of gold/ton of coal may retain up to 72 000 g (2200 troy oz) of gold. The estimation of the inventory implies the determination of the concentration of carbon in a tank and of the gold content of the species contained in the tanks. This paper assesses the errors associated with the sampling of CIL tanks to measure these concentrations and describes the impact of these errors on the estimation of the gold inventory in the CIL tanks of the Agnico-Eagle Mines Limited Lapa concentrator. (C) 2010 Elsevier Ltd. All rights reserved.