DENVER -- The 7NEWS Investigators have uncovered a chain of Colorado gas stations apparently cheating customers at the pump. And after 7NEWS started digging, the state stepped in and fined the owner of more than 20 Colorado gas stations.

The settlement agreement exposes a gas station operator playing games with your gasoline.

7NEWS learned about this after a veteran driver of gasoline tankers spoke out, blowing the whistle on his former employer.

"I wouldn't come to you if I didn't have the evidence," said a former Western Convenience Gasoline truck driver. "The public's being deceived … You watch people at the pumps and they're pumping gas and you know they're not getting what they think they're getting. It's not a good feeling."

"Simply, they're loading 85 octane and delivering it into the 87 octane and selling it as 87 ... Nobody really knows," he said.

Using hidden cameras, 7NEWS followed the trucks for several days from the filling yards to more than a dozen Denver-area gas stations.

"It's a practice that was so common at that company, and I feel the owner is so greedy that it's a hard practice for him to get away from, until he's caught," the truck driver said.

According to the driver, and documents viewed by 7NEWS investigators, Western Convenience Stores' truck drivers are loading regular 85 octane and dropping it into mid-grade tanks at Western Convenience locations throughout the Front Range.

The first time the driver was told to move 85 octane to the 87-octane tank, he said he "looked at the trainer and said, 'You can't do that, that's downgrading, that's contamination.'"

He said the trainer told him, "Well, we do that here all the time."

So that means if you paid an extra 10 cents for mid-grade unleaded at a Western Convenience Store, you may have wasted your money, because in at least a dozen cases in 24 days, the gas in the mid grade tanks was the very same as the gas in the regular tanks.

The driver 7NEWS talked to said he complained to his supervisor.

"I said, 'I'm not comfortable with that.' He goes, 'Well, you have to do it, that's your job.'" I said, 'You're asking me to steal from people?' 'Well, no we're not doing it, he's doing it. We're just getting paid to do a job,'" the driver said.

He said the "he" that his supervisor was referring to is the owner.

7NEWS Investigators obtained 12 documents supporting the former driver's claim.

According to one document, on one day, the Western Convenience driver purchased 9,002 gallons of regular unleaded gasoline. The receipt shows it was 85 octane. It also shows the driver split the load -- 7,002 gallons of the 9,000 gallons went into the regular unleaded tank and the remaining 2,000 gallons went into the "M" or mid-grade tank.

"I'm disappointed to see this happening," said Dick Piper, the director of the agency responsible for regulating Colorado's gas stations. "We do know that part of this was intentional."

That's why the state followed 7NEWS' investigation with action against Western Convenience Stores, citing the owner for 12 violations in just 24 days. On all 12 receipts, drivers documented pumping regular unleaded into mid-grade tanks.

Piper said what the gas station owner was doing was against the law.

The settlement agreement said the gas station operator admits breaking the law for the "delivery and sale of regular unleaded as mid-grade unleaded gasoline."

The owner of Western Convenience Stores, Hossein Taraghi, admitted it on paper but denied it in front of the 7NEWS camera.

"I am telling you that this is false accusation," Taraghi said.

Taraghi owns and operates nearly two dozen Western Convenience gas stations throughout Colorado.

When 7NEWS Investigator Tony Kovaleski showed him the documents and said, "The documents right here show you violated state law 12 times in 24 days ..."

Taraghi responded, "No, it's not violation."

"It says you purchased 85 unleaded with ethanol and your driver put it in the unleaded and the mid-grade unleaded. It's right there on the paper," Kovaleski said.

"That's not correct," Taraghi said.

"Your driver lied?" Kovaleski asked.

"Yes, he does," Taraghi said.

Taraghi signed the document acknowledging 12 violations and agreed to pay a $6,000 fine, promising to immediately discontinue the practice. But he also said his former employee and the state's investigators are wrong.

"I have never put unleaded gasoline in mid-grade gasoline. If there was a mistake, I have corrected it," Taraghi said.

But state investigators say that line of logic is simply not plausible. Taraghi's own paperwork shows five different drivers at five different stations pumped regular unleaded into mid-grade unleaded tanks -- 12 times in a 24-day period.

"So Mr. Taraghi, you are saying you've done nothing wrong here," Kovaleski said.

"No, nothing wrong. Absolutely nothing," Taraghi said.

His former driver said it can't just be a mistake.

"He's left a trail of evidence. It can't be a mistake," the former driver said.

That former driver quit working for Western Convenience after just two weeks on the job. He told his supervisor he could not continue to deceive the public.

Part of the problem is that the state rarely tests octane levels at gas stations. Western Convenience stresses it has passed every octane test. But a review of the records shows on average that the state checked a single mid-grade tank once every four years.

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