A method for detecting the presence of precipitants in a hydrocarbon stream, the method comprising introducing at least a portion of the hydrocarbon stream into a measurement chamber of an NMR measuring device, assaying the fluids in the chamber with proton nuclear magnetic resonance to obtain NMR signals, and processing the NMR signals to detect the formation of precipitants in the hydrocarbon stream. The method may be carried out at first and second locations, and NMR signals obtained at the two locations compared to detect precipitation of precipitant between the two locations. A method of monitoring the water content of a hydrocarbon stream in a flowline comprising introducing at least a portion of the hydrocarbon stream into an NMR measuring device, measuring a baseline NMR water signal of the hydrocarbon stream and comparing subsequent NMR water signals with the baseline NMR water signal to detect changes in the water content of the hydrocarbon stream.