David Koch - American businessman, philanthropist, political activist, and chemical engineer.

Despite the precipitous fall in oil prices in recent months, the fortunes of many of America's top oil magnates have actually grown, according to Wealth-X's ranking of the wealthiest U.S. oil barons.

Topping the list, David and Charles Koch, whom each boast a net worth of almost $45 billion making them the richest oil tycoons in the U.S. and the world, saw their wealth grow by 7 percent since last June – when the oil rout began.