EDISON - Some gas stations and convenience stores in New Jersey are selling obsolete, contaminated, even used motor oil, according to an exclusive Kane In Your Corner investigation. The State of New Jersey has done almost nothing to regulate the industry. Also, because many gas stations are leased to independent operators, the name on the sign outside does not guarantee that quality oil is sold inside.

News 12 New Jersey's Walt Kane offers some advice, based on his conversations with experts.

Look for the API Seal of Approval: Quality motor oil generally carries a seal of approval from the American Petroleum Institute. Kane In Your Corner gave failing grades to MaxiGuard, Black Knight, US Economy and US Spirit. None had API seals.

Check the API Service Classification: This is not a time when "A" is the best. The current classification is "SN." Some oils tested by Kane In Your Corner were labeled "SA" or "SB," making them suitable only for cars built in the 1930s or before. Others had no service classification, meaning there is no way to know what you are buying. "The SN, the SA, a lot of people don't know what that means," says Kenny Wenzel, a long-time mechanic, "But that label is there for a reason, to protect the consumer."

Look for the W: Each car requires a certain type of oil (like 5W-30 or 10W-40). You'll find it in your owner's manual or printed on the oil cap. Half the oils that failed Kane In Your Corner's tests were labeled either "5-30" or "10-40," with no "W." W" stands for "weight," which is how viscosity is measured. A motor oil maker which puts no "W" on the label can claim it never said its oil was a certain weight. Sometimes companies will claim the numbers are part of the product name. In the case of US Economy, the manufacturer claimed "5-30" meant the weight could be anywhere in between those numbers. Either way, it's probably not what you think it is.

Take a Whiff: Before putting an unknown brand of oil in your car, open the cap and make sure it smells new. A harsh, burned odor is a sign of waste oil being resold, says Tom Glenn, president of the Petroleum Quality Institute of America. "We have opened bottles and you can smell alcohols in them, materials that are clearly not oil." he says.

Look at the Color and Consistency: "We use a lot of different oils here," Wenzel says. "All of them are nice and gold and clear and see-through." By contrast, one of the oils Kane In Your Corner tested was almost black and cloudy, which Wenzel immediately pegged as likely being used oil. Lab tests confirmed it was likely waste oil being re-sold.