You might have noticed that some gas stations occasionally offer specials on unleaded 88 octane gas—also known as E15—which contains 15 percent ethanol. Ethanol is an alcohol that’s derived from corn.

Matt Webber is an experienced personal finance writer, researcher, and editor. He has published widely on personal finance, marketing, and the impact of technology on contemporary arts and culture.

Terms apply to American Express benefits and offers. Visit americanexpress.com to learn more. When it comes to car rentals, it's key to be aware of your credit card's inclusions and rental car ...