Cone penetration testing (CPT) was used to determine the void ratio and compressibility of Holocene peat present in the coastal–deltaic plain of the Netherlands, to explore its application for mapping the subsidence potential of this low-lying area. CPT sounds the mechanical behaviour of subsurface layers when penetrated with a cone, and is the most widely used site investigation method in the Netherlands. In this study 41 peat layers in the coastal–deltaic plain were sounded, and subsequently cored for determination of peat type, organic matter content, degree of decomposition and void ratio. The results revealed that cone resistance depends on the void ratio of the peat layer. The compression parameters coefficient of volume compressibility (mv) and compression index (Cc) were derived from this. The results further revealed that the compressibility of the peat increases with increasing organic matter content. It is concluded that for mapping the susceptibility of the coastal–deltaic plain to future subsidence by peat compression, CPT has the potential to become a useful tool, as thousands of CPTs are conducted in the Netherlands each year, and their logged measurements are stored in a freely accessible national database.