Reliable measurements of oil-in-water (OiW) content is essential in the oil and gas industry. The current OiW analysis techniques deployed in the industry need frequent calibration and mostly depend on optical access to the sample. They are also limited in providing a thorough compositional examination of the oil content. Nuclear magnetic resonance (NMR) is a well-established analytical tool across a wide range of different fields. For the OiW analysis, NMR can provide a self-calibrated measurement, does not require optical access, and allows for quantitative analysis of aromatic and aliphatic hydrocarbon content at the ppm level. Here, a fully automated prototype combining a custom-built solid-phase extraction (SPE) platform for sample pre-concentration and a benchtop NMR spectrometer for quantitative OiW measurements is designed, built, and demonstrated. The novel automated apparatus has significant potential for field deployment and provides a reliable and reproducible analysis of OiW content consistent with common reference methods.