Shale swelling is particularly problematic in the oil and gas exploration sector, as environmentally friendly water based muds are invariably used during drilling operations to lubricate the drill bit and carry cuttings back to the surface, and commonly the oil/gas reservoir will have a shale-based cap-rock which has high swelling clay content. In this experiment we will study the hydration of the commonly used clay swelling inhibitor tetramethylammonium (TMA) under oil-field conditions of up to 120C and 600 bar (equivalent to 4km burial depth), in both birne and synthetic clay. We will use isotope labelling of the TMA to ascertain both the local structure and also any propensity to for aggregates. We feel that NIMROD is ideal for this experiment as it will allow us to determine both the local hydration structure and also the clay hydration state.