The National Aeronautics and Space Administration has claimed that top Google executives used up to $5.3m worth of discounted jet fuel from the federal government which they weren't entitled to buy.

According to a Nasa report, inspector-general Paul Martin revealed that the tech giant's senior executives' "unwarranted" jet fuel discount is worth between $3.3m (£2m, €2.4m) and $5.3m.

However, Nasa says that the jet fuel purchases for Google's private planes were due to an internal government "misunderstanding" rather than any intentional misconduct from the company.

He also emphasised that while the taxpayer and government didn't necessarily lose any money, the Google executives "nevertheless received a monetary benefit to which it was not entitled," and the arrangement "engendered a sense of unfairness and a perception of favouritism."

H211 operates aircraft for Google co-founders Sergey Brin and Larry Page, and Google Chairman Eric Schmidt.

According to Pentagon reports, H211 bought 2.3 million gallons of jet fuel since early 2009.

It paid an average $3.19 per gallon, which is 25% below the price paid by corporate members of a non-profit fuel coop during this period.

Nasa said in the report that the discount fuel arrangement ended on 31 August this year after the Pentagon became aware that H211 was using the fuel for nongovernment flights.

"We are currently reviewing the report," said Ken Ambrose, an executive with H211.

How Google Got a Discount

Nasa said that it signed a deal with Google in 2007 to let the tech group's executives base their private jet fleet at Moffett Federal Airfield, a NASA-run facility a short distance from Google's headquarters.

The private air fleet recently included seven jets and two helicopters.

As part of the arrangement, alongside an arm of the Pentagon which controls fuel at the airfield, Nasa allowed Google executives to buy jet fuel at government prices, which are discounted from market prices and don't include state and local taxes.

In exchange, the Google executives agreed to provide free flights to NASA for research purposes.

However, Republican Senator Charles Grassley for Iowa has said, in response to the allegations which are backdated to 2007, that the "obvious remedy would be for Nasa to seek repayment for the taxpayers for the fuel benefit."