In this work, we report on pressure induced structural changes in crystalline oligo(paraphenylenes) containing two to six phenyl rings. Revisiting the crystal structures at ambient conditions reveals details in the packing principle. A linear relationship between the density at ambient conditions and the number of phenyl rings is found. Energy dispersive X-ray diffraction has been performed in a systematic study on polycrystalline powders of biphenyl, paraterphenyl, p-quaterphenyl, p-quinquephenyl and p-sexiphenyl under hydrostatic pressure up to 60 kbar. Our investigations not only yield pressure dependent lattice parameters and hints towards pressure induced changes in the molecular arrangement, but also allow for an analysis of the equations of state of these substances as a function of oligomer length. We report the previously unknown bulk modulus of p-quaterphenyl, p-quinquephenyl, and p-sexiphenyl (B0 = 83 kbar, 93 kbar, and 100 kbar respectively) and its pressure derivative (B0' = 6.4, 7.5, and 5.6). A linear dependence of the bulk modulus on the inverse number of phenyl rings in the molecules is found.