One well known method to establish important structural determinants of lipid bilayers, is the Luzzati method [1]. Here lipid molecular length and area are calculated from the excess water point and the unit cell spacing, determined by x-ray diffraction of a swelling series. It has been found that this method often results in larger area per lipid values than those found by other methods. Data are presented here demonstrating that this is at least partially due to the sensitivity of this method to sample preparation. Different sample preparation methods influencing bilayer alignment and bilayer defects, were investigated, Freeze-drying in the capillary with no or minimal subsequent mechanical mixing, lead to area per lipid values that are in general agreement with those found in literature: 78.7+/-2.0 Angstrom (2) for dioleoylphosphocholine (DOPC) at 25 degreesC, and 75.3+/-2.7 Angstrom (2) for dipalmitoleoylphosphocholine (DPolPC) at 15 degreesC.