Abstract: Vertical axisymmetric structures have found a variety of applications in offshore engineering, including oil storage tanks, production platforms and so on. The present paper describes an efficient calculation procedure for determining the interaction of such structures with the surrounding ocean. In particular, numerical calculations are explicated for:-wave forces and runup for a fixed structure,-added-mass and damping coefficients for an oscillating structure,-earthquake loading in terms of base shear and overturning moment,-motions of a floating structure.The approach used is based on a boundary element method involving an axisymmetric Green's function, and exploits the structure's ax.i symmetry to provide a highly efficient computational procedure suitable for carrying out on a desk-top computer. Results are presented for surface-piercing conical structures under various loading conditions.