Accurate detection of scale inhibitors has always been vitally important to monitor scale treatment during oil and gas production. However, there remains an ongoing challenge to analyze scale inhibitors at low concentrations, especially with polymeric scale inhibitors. This paper presents an assay method designed to detect all types of scale inhibitors, especially at low concentrations, and an expert program developed to guide the method. The program guides the preparation of a field brine barite solution at a fixed barite super-saturation. Scale inhibitor concentration is then measured via the method of standard additions, assuming a linear relationship between the scale inhibitor concentration and the logarithm of barite induction time. Seven different scale inhibitors, including phosphonates, carboxylates and sulfonates, were detected in two typical synthetic brines at low concentrations. In addition, this assay method has also been applied to scale inhibitor detection in actual field brines. In general, this easily-implemented method can directly detect the residual level of any scale inhibitors in field brine within the range of about 0.3 – 100 mg/L active. Emphasis in this paper is on low concentrations. Measurement of low concentration scale inhibitors not only help to monitor scaling tendency but also effectively prevent overuse of scale inhibitors and thereby protects the environment and saves money. This is the first method that can detect all scale inhibitors at extremely low concentration. Field applications, strengths, and interferences will be discussed using laboratory and field examples.