A general procedure for the analysis of curved or flat, thin two dimensional gas cavities such as thin compressor or engine manifolds or so-called thin shell type muffler elements, which can efficiently utilize the limited space of hermetically sealed compressors or small engine compartments, was developed. The basic assumption is that the thickness of the cavities is sufficiently small compared to the shortest wavelength of interest. The two dimensional inhomogeneous wave equation, which takes nonuniform thickness into account, is expressed in two dimensional curvilinear coordinates by the application of Hamilton’s principle. Four pole parameters are formulated from the pressure response solutions using the modal series expansion method and orthogonality property. Three gas cavities with simple geometries including a cylindrical thin cavity, a thin disk cavity and a thin spherical gas cavity are analyzed as examples. The convergence of the modal superposition is investigated. The transfer function of the thin disk cavity case is measured experimentally and compared to the theoretical results for verification. Because the back pressure at the valve location of a compressor or engine discharge port is an important issue for practical design applications, the input port impedance of the thin disk cavity from both theoretical and experimental approaches is compared. In addition, this particular thin disk model is successfully applied to a specific compressor head cavity. Both theoretical and experimental results are presented in this paper. Finally, active pulsation cancellation in the thin gas cavity can be achieved with the assistance of the above modeling procedure.