The comparative fuel bills for the three cars were: E10, $105; premium, $105.91; and regular unleaded, $100.33.

Had we used thirstier six-cylinder cars or less-efficient used cars, the equation would probably have strengthened further in favour of unleaded and premium fuel.

During our test, unleaded petrol was priced at $1.30 a litre, which meant the three cents a litre less we paid for E10 amounted to a 2.3pc discount.

But our figures show that the car using E10 used 4.2pc more fuel than the car using regular unleaded fuel.

During city driving, the discount remained the same but we used 7.2pc more E10 than regular and 11.2pc more than premium unleaded.

Since our test, the drop in petrol prices has made E10 more attractive, because a three cents-a-litre discount translates to a 3pc discount if fuel is priced at $1.

Our findings contrast starkly with the claims made by some petrol distributors.

United Petroleum general manager David Szymczak says overseas studies find the fuel consumption difference between E10 and unleaded can be as low as 1pc.

United's E10 fuel has a higher octane rating (95RON) than that of other distributors.

"‘When you consider that you can get 3pc to 5pc better economy just by having the right air [pressure] in your tyres, it's a very minor issue," Mr Szymczak says.

Caltex spokesman Frank Topham says the fuel-consumption differences vary widely from vehicle to vehicle.

"It is such an individual thing with each vehicle," he says.

"People should check it out for themselves and see if they find any appreciable difference."

But the head of engine development for Porsche's Cayman sports car, Jurgen Kapfer, says there is no doubt E10 is less efficient. Kapfer should know.

He's just been through the certification process for Euro V, the fuel standard about to be adopted in Europe.

Unlike previous fuel standards, Euro V demands car companies use an E10 blend in their cars when they complete their fuel consumption test cycle.

Under the current standard, the published fuel-consumption figures are based on a test that replicates city and country driving using premium unleaded, or 95RON, fuel.

That's why Porsche published two sets of fuel-consumption figures for the Cayman at the car's global launch in Spain recently.

The first set was for the current standard, Euro IV, while the second set had fuel consumption for the Euro V standard.

Using E10, the base model Cayman's fuel consumption increases about 3pc, from 8.9L/100km to 9.2L/100km.

This is what Porsche's official press information says about the switch: "When homologating a car to EU5 [Euro V], the manufacturer must provide for a new fuel grade with a higher share of ethanol.

"Displacing the same volume, such fuel has a lower calorific value than the fuel required for homologation to EU4.

"Hence, fuel consumption under the EU5 standard is slightly higher than with EU4 on the same carbon dioxide emissions."

The translation, according to Kapfer, is that the two are line-ball on saving the planet.

E10 emits less carbon dioxide but you use more of it, so the benefits are negligible.

The petrol companies appear to behaving an each-way bet on the topic of fuel efficiency.

On the one hand, they downplay the significance of E10's lower fuel efficiency; on the other, they are more than happy to talk up the efficiency of premium unleaded fuel.

They say premium unleaded is not only better for your car but noticeably more efficient than regular unleaded. By default, the same applies to E10.

BP says you can get up to 44 kilometres better range from a 70-litre fuel tank using premium unleaded instead of regular.

The tests, which returned an average 25-kilometre extra range, were based on a car that used 9.5L/100km for 15,000 kilometres under controlled conditions.

Our Camrys have an official Government measured fuel rating of 9.9L/100km, although all three cars performed better than their stickers claimed.

BP claims drivers can get up to 14.7pc more power (and an average of 7.7pc) from premium unleaded over regular.

The difference, according to BP, can be felt in better responsiveness and acceleration when using premium fuel.

To put that to the test, Drive put each of the three Camrys through a series of acceleration tests, including the time to 100kmh and a quarter-mile run.

The results were inconclusive, with all three cars achieving almost identical times for the traditional quarter-mile run.

Petrol companies say premium fuel works better because it has better cleaning properties, which means your engine is less prone to carbon deposits on your engine's fuel-intake valves.

BP says another benefit of premium is fewer exhaust emissions, particularly of sulphur, and up to 15pc less nitrogen oxide and hydrocarbon emissions than regular fuel.

Drive spoke to senior mechanics who backed up BP's claims about the benefits of using premium unleaded.

They told us there were visible differences between engines that had run only on premium petrol and those that had used regular fuel.

But they also had concerns about E10 and the effect it has on engines.

Some reported problems with catalytic converters in the muffler system, which can get clogged by these deposits and deteriorate.

In the US, experiments with E20 fuel (20pc ethanol) caused significant problems with catalytic converters.

In March, a General Motors spokesman told USA Today that in a GM test of E20 in Australia, "40pc of the vehicles sustained damage [to the catalytic converter], which allowed essentially unchecked tailpipe emissions".

Those concerns have been echoed in community attitudes to ethanol.

A national survey in 2005 found that six out of 10 people had reservations about ethanol fuel.

BP spokesman Chandran Vigneswaran dismisses suggestions that cars running E10 will not perform as well as those on regular unleaded.

"There is absolutely no reason to expect any negative effects," he says.

There have also been concerns about the air-quality benefits of E 10.

A Victorian Government study of ethanol found that E10 produced lower amounts of carbon dioxide and volatile organic compounds than regular petrol but produced more particulate matter and nitrous oxide, which is a precursor to smog.

Engine performance, fuel consumption and pollution are only part of the E10 argument, though.

Advocates of ethanol-blend fuel say E10 helps reduce greenhouse gases.

BP, which is replacing regular unleaded pumps with E10 bowsers across NSW and Queensland, estimates a net reduction in carbon dioxide of "between 1pc and 5pc".

Caltex's Topham says the general accepted wisdom is a "2pc to 6pc".