The method of determining a principal point of sunglint (PPS) on the ocean surface by observation from geostationary orbit is described. To find a PPS first a nonlinear equation is solved numerically, and then from one transformation the coordinates (latitude and longitude) of the PPS are obtained. The diurnal, seasonal and annual excursion of PPS are investigated. The entry parameters of the problem are the time t and longitude of satellite phi(sat). The contour of the Sun disk image and its sizes on a smooth ocean surface are studied. This method of finding PPS is then tested upon the Earth's image recorded from Meteosat satellites.