ESDU Struct 01.01.24 provides a series of theoretically derived graphs from which the buckling load can be determined, each graph being for a particular value of a stiffness parameter. The graphs plot contours of non-dimensional buckling load on a grid defined by the exposed length of the piston rod on one axis and the length of the cylinder containing the fluid on the other axis, both lengths non-dimensionalised by the jack length (that is the length of the cylinder and the exposed piston rod). The stiffness parameter is the root of the product of the ratios of the moduli of elasticity of the materials of the piston rod and the cylinder and of the moments of inertia of the cross-sections of the piston rod and the cylinder about an axis perpendicular to the plane of bending. The theory assumes the piston rod and cylinder are uniform along their lengths and that their section centroids are initially aligned. The piston rod is taken to be simply supported at the piston and at entry to the cylinder, and the jack is treated as pin jointed at the two ends. A worked example illustrates the use of the curves.