New concepts of hull forms with characteristics of low motions in waves, a big displacement and simple hull structure have been developed. They are most ideal for the floating production, storage and offloading units (FPSO). Two new concepts, a mono-column type (MC type) and a double moon pool type (DM type) were introduced in the former paper read at OMAE (1989). This paper will introduce the design of MC type FPSO and the model test in waves for the improved mono-column hull, which has more displacement and keeps the motion in waves almost same as the former model. The MC type FPSO has a low frequency response for pitching motion as a semi-submersible has. Such a pitching motion was reduced by the open type anti-pitching tank. The pitching motions in waves of the MC type FPSO and semi-submersible type floating production facility (FPF) were calculated in the typical oil fields in the world and the performances were compared through a year. It was confirmed that the MC type FPSO will be operated even in the North Sea with the same performance as the semi-submersible type FPF. The MC type FPSO will be most suitable for the production testing, early production and production for small oil fields.