It looks like a regular fuel pump, digits ticking over predictably as a driver fills up his car - until the figures suddenly skyrocket by 180 per cent.

That was the experience of astonished Sydney taxi driver Khairul Bashar at a petrol station in Penrith, where he filmed the price gauge unexpectedly surging from $15.29 to $42.97 in under a second.

He claims it was the second time it had happened to him at 7-Eleven bowsers within three weeks - only this time he was filming the bowser on his phone as a precaution.

“This had never happened to me before in 25 years of taxi driving,” he said.

“But it could be happening more often as people don’t usually monitor their bowser closely. I want to warn people to watch out when they are filling up.”

Mr Bashar said the first time it happened was on April 30 this year with pump eight at the 7-Eleven service station on Aspen Street, South Penrith. He claims the price leaped from $1.52 to $25.70.

When he turned off the pump and challenged the charge, he claims staff accused him of making it up and threatened to call police on him. Mr Bashar later reported the incident to police himself.

His subsequent complaint to 7-Eleven's head office was fobbed off with an email that included the line: "Regarding your complaint at our (Name of Store) Store, a Third Party Technician has attended on the 07/05/18 and they did not find any fault with the pump".

On the second alleged occasion at the main Penrith service station off North Road on May 22 this year, Mr Bashar captured video of the moment it spiked and even had a witness in another customer, who has confirmed his account to 9News.

Yesterday, 7-Eleven responded to his video and second complaint in an email. The email said it had sent a technician who "confirmed the pump is within tolerance, however a software issue with the dispenser was found" at the store.

The company asked for Mr Bashar’s address so it could send him a $43 gift card.

"It's not just about my money," Mr Bashar said. "I want to know if this is happening to other unsuspecting customers throughout the country."

He said his tank was not filled up with fuel to match the total amount charged on either occasion, making it unlikely the surge was a catch-up glitch.

Mr Bashar was filling up his taxi with LPG when the incidents allegedly happened.

When two LPG pumps from the same bowser are being used simultaneously, the one that started later may flow slower until the first one finishes. However, that doesn't result in extreme price surges.

In a statement, 7-Eleven said: "The two LPG pumps the customer experienced an issue with were inspected following each complaint and according to our technical subcontractors, found to be within the National Measurement Institute's (NMI) level of tolerance.

Following one of the customer's complaints Fair Trading NSW visited the site, undertook three independent tests, and gave the pumps a clean bill of health. However, clearly the customer's experience highlighted a problem with these two LPG pumps, which we investigated further and rectified."

Mr Bashar said he has reported his experiences to the Australian Competition and Consumer Commission, Fair Trading NSW and the National Measurement Institute.

Meanwhile, the NRMA recommends all motorists to keep their eyes on the bowser and also to check their own fuel gauge and ensure it corresponds with the amount of fuel they have added.