1869: The Charles, generally recognized as the world's first oil tanker, leaves the United States bound for Europe with the equivalent of 7,000 barrels of crude.

The Charles, home-ported in Antwerp, Belgium, carried its cargo in 59 iron tanks below decks. Earlier, oil was transported across the ocean in actual wooden barrels, each capable of holding only 42 gallons, which severely limited the carrying capacity of individual ships – but also established the "barrel" as oil's unit of measurement.

The Charles' tanks were configured in rows in the ballast to assure the ship's stability. It saw service between 1869 and 1872.

If the Charles was the world's first oil tanker, though, it was not, strictly speaking, the first tanker. Three weeks before the Charles weighed anchor, the British brig Novelty arrived in Boston carrying 84,000 gallons of molasses stored in bulk in similar tanks.

Since then, as the world's dependence on carbon-based fuels has mushroomed, tankers have played a critical role in both war and peace.

During World War II, they carried oil from American refineries to supply the Allied forces in both the European and Pacific theaters. The T2 oiler was the workhorse of the tanker fleet, and a highly prized target for both German and Japanese submarine commanders.

Today, the tanker remains the primary means of transporting oil in bulk, and almost half the ships at sea at any given time are of this type. Overall, as of 2005, oil tankers comprised just under 40 percent of the world's merchant shipping fleet.

The largest modern supertankers – the biggest ships ever built – carry in excess of 320,000 deadweight tons (roughly 2 million barrels) of crude, petrochemicals and a variety of other liquid cargo. In 2005, 2.42 billion metric tons of crude oil and refined petroleum were shipped by tanker.

Moving enormous amounts of oil entails obvious environmental risks, and accidents, when they've occurred, have been spectacularly destructive. The Exxon Valdez, which ran aground in Prince William Sound, Alaska, in 1989, resulted in 10.8 million gallons of crude being lost. Although there have been much larger oil spills, the Exxon Valdez incident remains one of the most damaging because of the particularly sensitive nature of the surrounding environment.

Source: Various