Optical, DSC and X-ray studies show that C-n H2n+1 O C-m H-2m OH (n = 16; m = 4; n = 18 and 20, m = 2 and 3; n = 22, m = 3) /aqueous H3PO4 systems exhibit mesophases in the order middle - viscous isotropic - lamellar - gel. The low temperature gel displays characteristically the chevron pattern due to an undulation instability of bilayers; it is possibly caused by hydrocarbon chain elongation and stiffening.