The voltage stability problem has been associated with environment questions and lack of financial resources for transmission system expansion. This reality together with the load growth makes the electrical system to be subject of heavy loadings, what can lead to situations of voltage collapse. The development of methods for evaluation of transmission network loading became necessary and indispensable in order to correct operation of the system under heavy loading conditions. In an international force-task report it is stated the need for analytical tools capable of verifying the voltage control action adequacy in the real-time operation. This work reports the development of a computation tool able to evaluate the effect of voltage control actions on the voltage itself. It is based the linearized load flow equations, including control and limit equations judged pertinent. The tool establishes a sensitive matrix, named [VCS] for voltage control sensitivity matrix, that relates the controlling variables and the controlled voltages. Through the analysis of the sign of each diagonal element, it is possible to know whether a specific control action is adequate or not. Moreover, the off-diagonal elements represent the interdependence among the voltage controller devices of the power system under analysis. The sensitivity matrix also allows the calculation of control actions necessary to move the operating point from an unstable area, or near by, to a secure operating region where all voltage control actions would have the expected effect. The results obtained with the voltage control sensitivity matrix applied on real and test-systems was qualitatively coherent with those calculated by analytical, iteractive by Newton-Raphson and/or continuationiteractive solution of power flow equations, validating the proposed method. The [VCS] dimension is proportional to the number of buses with controlled voltage in the system area under analysis. The matrix is not sparse and when there are a large number of voltage control equipments, its immediate analysis may be complex. Therefore, an analysis based on eigenvalues and eigenvectors associated with [VCS] matrix is used in order to identify voltage control action with opposite effect. In this case, the analysis is focused on negative eigenvalues. The identification of conflicting controls existence of any system area under analysis is a by-product. The voltage control sensitivity matrix computation and analysis are performed extremely fast. Therefore, the computational effort does not constrain its use in real-time operation.