After crude oil extraction, separation and treatment are probably the most important stages within different oil and gas business processes. Efficiency to separate crude oil from water and gas is directly related with production outputs and profits of oil companies. Ecopetrol S.A. being Colombia’s national oil production company has many different production facilities, being the Superintendence of Castilla – Chichimene one of the largest ones, producing a third of the total oil amount produced by Ecopetrol which borders up to 560.000 barrels of oil per day. The present study develops a reliability and availability analysis of Castilla 2 crude oil treatment station, which is the leading separation plant of the Superintendence, having paramount relevance on final oil production rates. The aim of this work is set on the identification of critical bottle necks and underperforming equipment within the process that can affect the overall availability of the treatment station, developing a model able to provide valuable information for decision making processes related with the sustainability or improvement of current production goals through the assessment of achievable availability and reliability values. In order to develop a realistic analysis, recognition of critical equipment is made and its results used to propose a plant grouping model based on functional blocks, systems and main processes. Moreover, real maintenance information has been retrieved from different existing databases and used to construct and define parameters of individual failure distributions on each one of the equipment selected for the study. A reliability block diagram capable to describe functional relationships of the elements, systems and processes of the treatment plant was developed. Through this model, quantitative analysis and measurements were made allowing identification of elements and combinations prone to generate major downtime. Several availability simulation were used to find sensitive points within the plant that can affect overall production goals, while proposed actions and plant modifications were introduced into the model to assess their benefits and effectiveness towards production and availability improvement.