Las Vegas cab driver Gerardo Gamboa thought someone left a bag of chocolates in the back seat but the stash turned out to be cold hard cash.
Mr Gamboa was making a pick-up yesterday at the Bellagio when a hotel doorman noticed the brown paper bag and handed it to him.
At a red light the Checker Cab driver's curiosity got the best of him. To his surprise, he found six bundles of 100 US dollar bills totalling 300,000 US dollars.
The newspaper reports Mr Gamboa called his dispatcher and took the money to the company's main office, according to the Las Vegas Review-Journal.
Las Vegas police and casino officials were able to link the money to a well-known poker player they declined to identify.
It is unknown whether Mr Gamboa will receive a big Christmas tip.