Scale model experiments of roll decay in calm water and forced roll in a regular beam sea have been conducted on several ship typologies. A methodology for the estimation of the roll equation parameters, based on nonlinear least squares fitting to the experimental data has been developed and implemented in a computer code. The analysis of experimental data allowed to obtain informations on the different linear and nonlinear damping contributions, on the nonlinear restoring moment coefficient and on the effective wave slope coefficient. The conclusions highlight the validity of different damping models in simulating forced roll in waves. At the same time, the conclusions enforce the known problem of the dependency of the parameters on the frequency of the excitation, especially in the presence of large nonlinearity of the restoring moment.