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

The committee has examined and identified the degree of seasonal variation in the pattern of oceanborne oil shipments and freight rates in the major tanker trades.²

A monthly seasonal variation index for crude oil exports from the Arabian Gulf (past Hormuz) was computed.³ The average for the year was defined as 100. A significant degree of seasonal variation is evident from the data presented in Table H-1.

The seasonal index of oceanborne crude oil movements from the Arabian Gulf for the 1990 to 1995 period shows a seasonal high of 102.38 in December and a low of 97.05 in April—that is, a spread of 5.3 percent. The average index for the first five-month period from April through August is 98.21 and for December through March, 101.27. An average seasonal variation of 5 percent in oil shipments is not at all surprising and does not suggest a great seasonal impact on tanker demand. However, if tanker supply is in the inelastic range, the impact of seasonality on freight rates is considerable.

The seasonal variation indices for freight rates of very large crude carriers (VLCCs) trading from the Arabian Gulf to Rotterdam between 1970 and 1995 indicate a pronounced seasonal variation of considerable amplitude (Table H-2). These results support the notion expressed earlier that a small (5 percent) change in tanker shipments can result in a large (47 percent) change in freight rates, consistent with the supply inelasticities discussed in Appendix G.

In the case of Suezmax tankers (Table H-3), the same seasonal pattern is present, although somewhat moderated in that the maximum spread of indices is lower. Similar trends are observed for Aframax tankers (Table H-4). For both Suezmax and Aframax tankers, data for the period since 1990 are insufficient to permit conclusions to be drawn.

Data for product tankers trading from the Caribbean to the east coast of the United States are given in Table H-5. Despite the fact that such tankers are smaller and operate in totally different trades from the VLCCs, Suezmax tankers, and Aframax tankers discussed earlier, the impact of the seasonal pattern on freight rates is very strong.