This paper uses the technique of rheo-nuclear magnetic resonance (rheo-NMR) [reviewed by P. T. Callaghan, Rep. Prog. Phys. 62, 599-670 (1999)] to perform a systematic study of emulsion theology. Rheo-NMR uses NMR velocimetry to produce velocity maps, from which it is possible to quantify rheological parameters, with apparent wall slip being measured directly. The study is initially conducted on silicone oil-in-water emulsions. Xanthan gum, an important emulsion thickener and stabilizer in the food industry, is then investigated. Finally, the technique is applied to a commercial mayonnaise, which is a complex product comprising a concentrated oil in water emulsion with various thickeners and stabilizers in the continuous phase. Rheological parameters (based on either a power-law fluid or a Hershel-Bulkley analysis) and apparent slip characteristics are extracted from the velocity maps for these materials, across a wide range of shear rates. Comparison with conventional theological measurement and analysis is presented; reasonably good agreement is produced between the two methods. (C) 2004 The Society of Rheology.