An oil and gas well shaped charge perforator capable of providing an exothermic reaction after detonation is provided, comprising a housing (2), a high explosive (3), and a reactive liner (6) where the high explosive (3) is positioned between the reactive liner (6) and the housing (2). The reactive liner (6) is produced from a composition which is capable of sustaining an exothermic reaction during the formation of the cutting jet. The composition may be selected from any known formulation which is suitable for use in an oil and gas well perforator, typically the composition will comprise at least two metals such as to form a inter-metallic as classified by Hume-Rothery electron compounds and at least one further metal, which is not capable of an exothermic reaction with the reactive composition which is present in an amount greater than 10% w/w of the liner (6).