The conformational behavior of membranes derived from a new class of phospholipids, 1,2-dipalmitoyl-sn-glycero-phosphatidyloligoglycerols DPPG(x), is studied for the first time by FT-IR spectroscopy in the liquid crystalline and gel state. The phospholipids examined here are characterized by oligoglycerol chains of variable length in the headgroup, ranging from one (x = 1, DPPG(1) = DPPG) to four glycerol units (x = 4, DPPG(4)). The transition from the gellike to the liquid crystalline phase is monitored via CH2 and CD2 stretching bands as well as CH2 wagging band progressions. CH2 wagging bands are used to determine the relative amounts, i.e., integral values over the whole chains, of kink/gauche-trans-gauche, double gauche, and end gauche conformers in the acyl chain region. Information about the absolute amount of gauche conformers at a specific chain segment is obtained by a quantitative analysis of the CD2 rocking band region for phospholipid samples with selectively deuterated acyl chains. These latter data are combined with the results from an independent H-2 NMR study on the same compounds, which allows a distinction between the overall chain order and the local conformational order of the phospholipid chains. In addition, results from solid state P-31 and C-13 NMR studies are presented which provide additional support for the conclusions based on the FT-IR data. The present work clearly shows that the conformational and structural properties strongly depend on the headgroup structure and hydrophilicity, sample composition as well as sample temperature. The derived data are discussed by considering related phospholipid systems, such as DPPC, to demonstrate the particular impact of the headgroup length and hydrophilicity on the ordering characteristics of the acyl chains.