The use of proton nuclear magnetic resonance (NMR) spectroscopy as an on-line continuous flow detector for liquid chromatography (LC-¹H NMR) is described. Flow inserts for electromagnet and superconducting solenoid magnets are described. Applications to fuel analysis are presented. LC-¹H NMR is shown to be an informative technique. The principle limitation is sensitivity. Conditions for quantitative flow pulse NMR measurements are presented. An average composition method for fuel samples (based on LC-¹H NMR) is derived. This method is shown to be of value in characterizing the aromatic fractions of low boiling fuels. Average degrees of substitution, number average molecular weights, and other quantities can be determined with this method. A theoretical description of flow NMR experiments is developed. The classical description of magnetization (based on the Bloch equations) and detailed physical pictures of flow are combined in computer simulations. Several examples are given and computer program listings are appended. / Ph. D.