Ternary diagrams have been used mainly in chemistry applications, and in geology for characterizing mineral components of rocks. In this study the ternary diagram called the Cusiana Well Performance Triangle is being proposed as a powerful well - reservoir surveillance evaluation tool. The main contribution of this diagram is to provide well surveillance engineers and managers with a tool that facilitates the decision making process.Decline in productivity is influenced by reservoir related factors such as fluid properties, rock properties, pressure depletion trend, GOR and WOR increase trends and physical skin build up, generated by different methods. Usually organic substances, inorganic scales or very fine materials are transported and/or deposited in thenear wellbore region, hence, high decline rates can be observed.In this study a well performance analysis and a formation damage evaluation were conducted using nodal analysis. The final delivery was the quantitative contribution of the main factors influencing the well productivity. The results are presented graphically in the ternary diagram referred to as Cusiana well Performance triangle.The position of a well in the triangle indicates the factors that are influencing well performance. The triangle is used as a first step in understanding well performance with a view to wellwork candidate selection.Recommendations based upon the observed results can provide the operator with a reliable tool to implement a formation damage management strategy for the Cusiana field.