Studies of crushing crystals while viewing them under a microscope (＇＇stage-crushing＇＇ studies) were carried out on fracture-filling anhydrites from the Vulcan and Vanguard gasfields in the UK sector of the southern North Sea. These studies were performed after the appearance of clathrate solids during microthermometric freezing experiments which indicated the presence of a gas component within the inclusions. After several attempts at a very difficult analytical technique, a series of photographs were taken of the process whereby the vapour phase in the inclusions expanded This indicated the existence of a gas under pressure in the inclusions. Gas chromatograph ic studies suggested the dominance of methane, and that the overall component is comparable to that of the southern North Sea gas reservoirs.