Xipilli smiled. "Oil is a fuel for the duece and a half, tank, and airplane, among other things. Without oil these cannot run. A Deuce and a half is a.... "mechanical" wagon without horses capable of carrying two and a half tons of equipment. It does not tire like a horse, and can run for days straight. A tank is a large, often slow metallic 'wagon' with a cannon, it can not be harmed by average guns. And the airplane, well obviously you have heard of foreigners taking to the sky in such contraptions, these are those devices."
Truly I could tell this man oil is more precious than anything and he would believe me, Xipilli looked at the kind king, he's lucky he met me, and not another person more willing to accept profit.
"Oil is quite common where I come from. The only reason it's slightly expensive is shipping costs. If you're interested... I can arrange for many of these things to be brought to you so you can have a more hands-on understanding of them."