Abstract: A barge (14) that stores liquid hydrocarbon (oil) from a producing facility (12) and offloads it perhaps once a month to a shuttle taker (40), is constructed for unmanned operation except during the once-per-month unloading. The barge has a permanent nonadjustable ballast (53, 54, 55) and has a solar powered system for communication with a central center for normal operation and emergency shutdown. The barge avoids a “hotel system” for a permanent crew (up to 50 people) by avoiding seawater ballast tanks, ballast pumps and related systems. The only person-operated equipment is an engine-generator set (142) and pumps (44), to be operated only during offloading for perhaps 3 days every month. The barge is unpowered except by solar energy or batteries, and is left unmanned except during offloading, so only temporary crew quarters are provided. The barge has a tank assembly (57) with rows of tanks connected in series so oil can be loaded and unloaded from the frontmost tank in each row.