Final answer:
The veins have the largest volume capacity within the vascular system, particularly the inferior vena cava.
Step-by-step explanation:
The vessels that contain the largest volume in the vascular system are the veins. Unlike arteries, which carry blood away from the heart under high pressure, veins carry blood back toward the heart under lower pressure. Veins have valves that prevent backflow and a larger lumen compared to arteries, allowing them to accommodate a larger volume of blood. In particular, the inferior vena cava is the largest vein and holds the most blood volume within the circulatory system.