Specific volumes of aqueous solutions of triblock (PEP) copolymers of ethylene oxide and propylene oxide at solute weight fractions 0.1 ⩽ w 2 ⩽ 0.39 were measured in the temperature range from 5 to 65 °C. Partial molar volumes V 2 per chain repeat unit, their temperature quotient ∂ V ́ 2 ∂T , and excess partial molar volumes V ̄ 2 E computed. The values of sol V ̄ 2,∂ V ̄ 2 ∂T and the absolute values ¦ V ̄ 2 E¦ decrease with increasing content of ethylene oxide units. The excess partial molar expansibility α 2 −0 E at infinite dilution for oligomeric homopolymers (PEO, PPO) were evaluated from reported data. They are positive and display a similar trend to V ̄ 2 E The values of V ̄ 2 E and α 2 −0 E are comparable to those reported for low-molecular-weight cyclic ethers. The results are taken to reflect the effects of polar and apolar groups on the supermolecular structure of water.