A fuel ship concept...
Venusian Light Replenishment Oiler
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In order to support their wide ranging Trading missions, the merchants of Venus often travel in convoys containing a few replenishment oilers. These ships rarely carry goods for trade, but by providing a group of Traders with fuel and other consumables they grant the Venusian tradeships independence from local retail prices, and greatly extend the reach of the Venusian Trade Fleets.