In the design of a floating oil storage system, especially of its mooring system, it is essentially important to accurately estimate the environmental forces. In order to evaluate the design values of wind loads, the characteristics of wind such as storm frequency, spectrum of fluctuating wind at the site were investigated based on the results of meteorological observations. Further, characteristics of wind loads such as the influences of shape of barge and hydrodynamic mutual interaction with adjacent barges were examined in detail by wind tunnel tests. As the results, the design values of the wind velocity and the wind drag coefficients were obtained with sufficient reliability by taking the above-mentioned factors into consideration.