In a stomach-churning example of how one man's trash is another man's treasure, thieves in New York are reportedly stealing used cooking oil left outside by restaurants and selling it as bio-fuel.

According to a special investigation by FOX affiliate MyFOX New York, the grease has become a hot target due to pumped-up gas prices and a growing demand for an alternative-fuel source — and it's got some people doing almost anything to cash in.

Investigators said that "people are stealing it left and right" and that the grease is so sought after, it's been dubbed "liquid gold."

It's no wonder. The price of the cooking oil, which can be converted into bio-fuel and used to power engines, has skyrocketed almost 400 percent since 2000. Restaurants that once paid to get the muck shipped away are now being paid almost $200 for one tank of used grease, according to MyFOX New York.

Thieves come — often in broad daylight — with a truck and hose and pump it out of special dumpsters.

Restaurant owners of La Parma II told MyFOX New York that the crooks have become so bold, they've had to set up surveillance cameras aimed at the garbage.

Click here for more on this story from MyFOXNY.com.