On-line analyzer systems are widely used in the Oil & Gas and (Petro) Chemical industry. They range from single component analyzers like pH analyzers to multi-component analyzers like gas chromatography and mass-spectrometers, from wet chemistry types to optical devices.

An online process analyzer is generally a complex system compared with other, more general-purpose types of process instrumentation. It often needs an additional sample preparation and disposal system, which might be difficult in its own right. Hence, system design often results in a measurement system that is less stable than traditional process instruments, thus needing more maintenance attention from better than average qualified maintenance staff.