In the mining industry, drilling is the main process through which new data (samples) is generated to upgrade confidence in predictive 3D models of geology and grade. For this reason, the generation of the drilling plan is a key activity to quantify the required data (number of meters) and its volumetric distribution to obtain a determined level of confidence in a known volume. There are different methodologies to define drilling plans; some of them take into consideration regular spacing between holes whilst others simply rely upon visual assessment to identify poorly sampled areas. Normally these practices are based on the level of experience of a team or a professional and do not necessarily include deposit variability in the outcome. Additionally, approaches do not include consideration of whether the drill plan will address the objective of the temporal requirements (ie within the five-year plan) of reducing uncertainty via data collection thereby supporting the priorities of the mine plan. Drilling activities generally represent more than 80% of the geology budget in a mining operation. Budget reduction and/or optimisation of the drill plan, whether in response to budget pressures or operational requirement for greater effectiveness, directly affects the drilling plan. The impact of reduction of meters to be drilled, or the postponement of meters into the future, results in the same outcome greater uncertainty than desired across the various stages of the mine plan. Faced with this common budget situation, can we as geologists inform management of the uncertainty and risk implications of this requirement? How effectively can we quantitatively support the requirements of our existing drilling plans? This paper describes the use of uncertainty models to support the generation of drilling plans at the Escondida mining operation. Uncertainty models take into consideration the confidence obtained from the simulation of both geological characteristics and metal grades. The definition of error limits for a defined volume within the deposit facilitates the understanding of required drill meters against acceptable error for both planning and mining operations. Examples of the impact that reducing the drilling plan has on the confidence in the resulting resource model are also discussed. CITATION: Cortes, M, Soto, L, Veliz, W and Williams, M, 2019. Drilling plan generation based on uncertainty models. Definition of uncertainty thresholds, error for a determined volume at Escondida Mine, in Proceedings Mining Geology 2019, pp 253259 (The Australasian Institute of Mining and Metallurgy: Melbourne).