Formula One fuel's hidden 1%: The best kept secret in sport?

The fuel used in Formula One cars is 99% the same as the kind pumped into the hatchbacks, saloons or estate cars seen on roads all over the world.

So what, exactly, is in that missing 1% that makes elite motorsport so special?

"That's what I keep in my back pocket, I'm afraid," Mike Evans, head of the fuel development program at Shell -- which is supplier to the Ferrari team -- told CNN's The Circuit ahead of this weekend's Hungarian Grand Prix.

"This is the special treatment we give to the fuel, to make sure it gives the ultimate performance in the Ferrari engine, so unfortunately I'm sworn to secrecy on that one."

As well as keeping their secret formula out of the public's tanks, fuel suppliers also have to guard against curious rival companies.

"We go to extreme extents (of secrecy)," Evans explains.

"The fuel supplied is in our control the whole time, it'll be stored in a truck in Europe or in a funded area at the races.

"There will be security over there, and after the race we arrange for what's not been used to be disposed, locally adulterated, or returned sometimes back to our laboratory in Germany.

"I mean there is folklore -- and I've never witnessed this -- that people in the past used to go along and drill on the underside of the drum and get a sample out.

"Obviously on the top of the drum it looked great and then you'd suddenly realize it felt a bit light.

"But those days are long since gone, so it is one of the things I would love to know how our fuels compare to our competitors'."

Much like athletes are subjected to drug tests before, during or after competitions, so too does the cars' fuel undergo a similar process to ensure it complies with regulations.

Formula 1

The FIA, motorsport's governing body, puts fuels through a rigorous test, while also regularly checking it over the course of a grand prix weekend.

"They do this 'blood' test -- the GC (Gas Chromatograph) test -- on it, like a fingerprint of all the different compounds that are in the fuel," Evans adds.

"The FIA are doing this 'blood' test to make sure that once the fuel has been approved, we don't surreptitiously put this compound X in the fuel and then use it at the races.

"They will come round twice over the race weekend. We monitor it from when we take the samples out of the drums, into the fueling rigs and into the car, to make sure that there's no contamination."

The stakes are high for Evans and his team, as any mistake can have huge implications for Ferrari and its drivers throughout the championship.

In 1997, Mika Hakkinen was stripped of his third place at the Belgium Grand Prix after the FIA ruled his fuel was not the correct formula.

"You could be disqualified or you could get a big fine," Evans said. "It's bad news, basically.

"It would be the team and the driver who would get the penalty -- so probably not Shell.

"If the team were fined, they would come and see us. The driver can face the penalty as well as the team, so we have to be very, very careful."