The laboratory experiments performed in two different wave basins are comparatively analysed with both spectral and statistical methods to verify and validate the wave data used in the following numerical study. Comparison has been made in the aspects of the main sea state parameters, the power spectral density, the joint distribution of wave heights and periods, and the marginal distributions of wave heights and wave periods, respectively. Meanwhile, some of the observations are also compared with the corresponding theoretical model predications. Furthermore, the directional spreading effect on the formation of extreme wave is discussed as well. In addition, the variation of dynamic pressure under the crest of nonlinear waves is measured in another wave flume. The vertical pressure profile of individual waves with the same crest height is investigated in regular and irregular sea states, and the influence of different types of nonlinearity on the dynamic pressure is discussed for extreme waves formed by both linear and nonlinear methods.