Stiction or high static friction is a common problem in spring-diaphragm type control valves, which are widely used in the process industry. Recently, there have been many attempts to understand, define, model and detect stiction in control valves. There are several methods for detecting stiction, but quantification of the actual amount of stiction still remains a challenge. This paper discusses briefly the definition and modelling of stiction. Then it demonstrates a new method to detect and quantify the actual amount of valve stiction using routine operating data. The proposed method is completely data-driven. No additional excitation or experimentation of the plant is required. (c) 2007 Elsevier Ltd. All rights reserved.