The NAS report gives a rate for serious casualties for the whole tanker fleet and not for major oil spills from "supertankers". The rate of major oil spills is much lower, as is indicated by the very next section of the same report.
Our own database shows that, based on the period since 1974, the actual percentage of "supertankers" suffering a spill of over 10,000 tonnes during their lifetime is, at most, between 2 and 4 per cent. Even this is an over-estimate, since the annual incidence of oil spills has dropped significantly since the 1970s.
International Tanker Owners Pollution Federation
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