By Jack Fink, CBS 11 News

DALLAS (CBSDFW.COM) – Felicia Allen got an unpleasant surprise when she filled up her car last year; the gas had water in it. “I had to take this car and pay $1,000 on it because the fuel injection got messed up because of the gas.”  That’s one reason state inspectors check the quality of gas at pumps around the state.

This past January, inspectors found water in the gas at the Get n’ Go station on Audelia Road in Dallas.  The manager told us he believes the fuel was delivered that way.

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And last September, the state found water in the gas at the McCorner gas station on Northwest Expressway in Grapevine.  A station representative says water got into the underground tank after the deliveryman forgot to put the cap on.

Brian McKevitt, a master technician at Sam Pack Ford in Carrollton says water in gas can wreak havoc.  “Worst case is you’d have to replace the engine, and that could range anywhere from $3,000 to $7,000 or up for a diesel, it would be way over that.”

Amador Hernandez is among the field inspectors testing the gas quality.   “If there’s water in it, it’ll settle to the bottom and you’d see a bubble.”

So how does this happen?

Stephen Benjamin, the director of the North Carolina department of agriculture’s standards division, says water can get into a gas station’s underground storage tanks if there’s a leak in the system.

It can also happen when gas is being delivered to a station.

Felicia Allen wishes she had known the state has a fuel testing program-when she discovered poor quality gas had damaged her car.

When asked if she knew she could file a complaint with the state and have them investigate that station, Allen said, “No, I didn’t know that. So I just took my losses and left and never went back.”

The state also tests the octane levels at 2500 pumps across the state each year.

Some cars will start knocking and pinging if the octane levels is too low, and state law requires stations to sell fuel at the octane level stated on the pump. Hernandez says, “If it’s posted for whatever grade it is, you need to make sure you’re getting that grade.”

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On the day CBS 11 followed him, Hernandez concluded many Fort Worth gas stations passed the test.  But state records obtained by CBS 11 show between January 2008 through the end of February of this year, there were 25 different gas stations in Dallas, Tarrant, Collin, and Denton counties that didn’t pass.

We found an extreme example, up in Denton, at the Chevron along I-35 and university.

Last November, the mid-grade’s 89 octane actually had a lot less than even regular unleaded – just 79 octane.

After conducting field tests, inspectors send the samples to a lab for confirmation. Hernandez says, “If it came back from the lab that it failed, then I would go back and do a re-inspection. If it failed on the re-inspection, then I would issue a stop sale.”

During a follow-up inspection the following week, the mid-grade 89 at the Denton station only measured up to 87.7 octane — and the premium 93 octane only tested at 92.1.

The station adjusted the pump labels to accurately reflect what was really in the pump — so it could continue selling the gas.  The manager declined comment.

Last year, 13 percent of octane samples statewide failed to match the tag on the pump.  The department of agriculture issued 46 violations.  Aside from the state tests, consumers really have no real way of knowing what’s in the fuel.

So we asked experts why there’s sometimes less octane than advertised?  They say most of the time, it’s not a problem with the gas itself, but the pump.

Texas consulted with Stephen Benjamin of the North Carolina standards division and other experts when it began the fuel quality-testing program. “Typically, what we see today is the pumps themselves may blend the product, or there’s a valve in the pump that switches those products, so it could be a mechanical problem, it could be a computer chip problem.”

Drivers may not care what’s causing the problem, but with prices this high, they absolutely want to make sure they’re getting their money’s worth.

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Consumers can file a complaint against a gas station with the department of agriculture on their website, or you can also call the agency at 1-800 TELL-TDA.