Sentence:  The dawn of the oil age was fairly recent. Although the stuff was used to waterproof boats in the Middle East 6,000 years ago, extracting it in earnest began only in 1859 after an oil strike in Pennsylvania....It was used to make kerosene, the main fuel for artificial lighting after overfishing led to a shortage of whale blubber. Other <WSD>liquids</WSD> produced in the refining process, too unstable or smoky for lamplight, were burned or dumped. 
Meaning of the word marked with <WSD> tags:  A substance that is flowing, and keeping no shape, such as water; a substance of which the molecules, while not tending to separate from one another like those of a gas, readily change their relative position, and which therefore retains no definite shape, except that determined by the containing receptacle; an inelastic fluid.