The P-wave modulus and porosity of samples from North Sea chalk reservoirs were compared to data from the Ocean Drilling Program. The ODP classifies pelagic calcareous sediments as uncemented "ooze", "chalk", "clay", "claystone" and "mixed sediments" or as cemented "limestone" and "mixed sedimentary rock". Here the P-wave modulus and the porosity are discussed for these sediments. Sorting of pelagic calcareous sediments depends on mixing between nannofossils (mud), clay, and microfossils. In hydrocarbon bearing North Sea chalk, microfossils may be filled with cement and mud particles mature to equant shape while the mud itself remains uncemented. Results show that sea bottom porosity varies between 55-80% depending on sorting. Clay rich lithologies may reach porosities below 10% by physical compaction, whereas clay poor ODP chalk cannot even be compacted to 30% porosity. Cementation may result in porosities of less than 10% irrespective of clay content, however some cemented samples may have porosities as high as 50%. North Sea chalk with mature mud may be compacted to porosities near 20%. The P-wave modulus can also be related to sediment classification. Mixing of nannofossils and hollow microfossils in ooze and chalk results in a relatively high P-wave modulus for a given porosity as compared to a pure nannofossil (mudstone) sediment. A higher clay fraction corresponds to a lower P-wave modulus for a given porosity and cementation results in a relatively high P-wave modulus. Notably, North Sea chalk with filled microfossils have a low P-wave modulus for a given porosity as compared to pure mudstone.