Double-Hull Tanker Legislation: An Assessment of the Oil Pollution Act of 1990 (1998)

Table E-1 shows the change in age from 1990 to 1994 on the basis of ownership category for vessels in the U.S. trading fleet. For government-owned vessels there was an increase in age of 0.38 year, but this was more than offset by the decrease of 1.02 years in the age of the numerous independent fleet and 0.99 year in the small oil company fleet. When figures based on the number of port calls are considered, rather than just the fleet itself, as shown in Table E-2, the change is more pronounced: 1.66 years average reduction, with a 0.35-year decrease for governments, a 1.49-year decrease for independents, and a 2.51-year decrease for oil companies. The new vessels are clearly making more calls on average than the older ones.

In looking beyond averages at size categories, it can be seen that the average age of government vessels has been decreasing for smaller vessels (<150,000 DWT [deadweight tons]) and becoming more diverse for larger vessels (> 150,000 DWT). The same broadly applies to oil companies. Independents show a split tendency, with old and young ships predominating in large sizes but few in the middle age bands, and a broad balance in the smaller sizes (see Table E-3).