A high‐pressure dilatometer capable of measuring volume changes of 2×10−6cm3is described. Fractional volume changes of 1 part in 104can be measured over a temperature range of −30–90 °C, and a pressure range of 1 bar (0.1 MPa)–3 kbar (300 MPa). The dilatometer is constructed out of a commercial high‐pressure valve and a compact home‐built pressure sensor. The system was specially designed to study lipid‐water biological systems. Preliminary studies on the lipid dioleoylphosphatidylethanolamine (DOPE) revealed the existence of phases not previously reported for this lipid.