Abstract: A mobile offshore platform in which a support structure receives interchangeable barges thereon for carrying out the different functions required in producing an offshore hydrocarbon reservoir. The mobile offshore platform includes a plurality of support legs extending into the water down to the ocean floor. Jacking mechanisms engage each support leg to raise and lower a negatively buoyant, open network platform structure relative to the surface of the water. A barge having a process plant installed on board is docked in position on the platform structure. A heave absorber disposed above the surface level of the platform structure engages the bottom of the barge to dampen vertical motion thereof. The platform structure and the barge are raised above the water to the required height, whereupon the platform structure is secured to the legs and the jacks may be removed for use on another platform.