Abstract VASPS (Vertical Annular Separation and Pumping System) is an innovative concept for two-phase subsea separation and pumping. The paper illustrates the installation, commissioning, and start-up of the 9,000 BBLD VASPS subsea unit, which was successfully brought on-stream in July 2001 in the Marimba Field (Campos Basin, Brazil). Introduction A large fraction of the exploration investment in all major oil companies is dedicated to deep and ultra-deepwater reservoirs. Even if the exploration is technically successful, the high production costs associated with conventional development schemes often makes such fields non-profitable. As a consequence, since the 1990s, many of the operators have been involved in the development of profitable and competitive subsea processing technologies to maximize production rates and recoverable reserves. VASPS (Vertical Annular Separation and Pumping System) is an innovative two-phase subsea separation and pumping system concept, which allows high capacity integrated separation and pumping equipment to be installed within a 30 to 36-inch conductor in a dummy well (Fig. 1). Installation and maintenance of the unit were conceived to be accomplished by using conventional subsea drilling and completion technology and equipment. VASPS technology has been developed in a phased approach [Ref. 1-10] addressing the various issues in a hierarchical manner. Phase 1 (1990-91) consisted of laboratory tests, Phase 2 (1993-95) in-land field tests at AGIP site in Trecate-Italy, Pre-subsea Phase (1995-97) in-land field tests at PETROBRAS site in Atalaia-Brazil, and the Subsea Demonstration Phase (1998-2002) in Campos Basin-Brazil. From a mechanical point of view the VASPS is based on standard subsea tree, casing and wellhead components. With reference to the stack-up arrangement (see Fig. 2), the VASPS Subsea Hardware designed for Marimba 1 is based on the following main components:FoundationFlowbaseMulti-bore and single-bore flowline connectorsSeparator composed of the pressure housing (6 joints, each 12 m long and 26-inch diameter), and the helix (6 joints, 12¾ -inch diameter)Head assembly and top plugESP and liquid discharge tubingRunning tool The control system is composed of a hydraulic power unit, subsea control module, master control station, subsea choke valve and level sensors. The electrical system includes the ESP with the shroud connected to the liquid discharge tubing, multisensor, power cable and wet-mateable connector, and variable speed drive. Detailed information is available in [Ref. 1] The system was totally assembled and tested in Aberdeen (Site Integration Test) before being transported to Brazil. Part of the hardware was re-assembled inland and tested at Macae-Brazil (Site Receiving Test) before the offshore installation. Pre-commissioning at Aberdeen The main objective of the Site Integration Tests (SIT), performed in Aberdeen during February 2000, was to check the feasibility of the proposed handling, assembly and installation procedures. Particular attention was given to the novel parts of the system or to those that had any sort of criticality during the offshore installation.