Plug-in hybrids, such as the Chevrolet Volt, have potential for saving a lot of gasoline, something their loyal owners love to brag about. That's what we've found among Web users on our own forums, where many are claiming they use even less gas than our formal tests have assumed.

These cars present a unique challenge because their fuel economy varies tremendously depending on how far each driver goes before they are able to return to an electric charger. The variation is much greater than the difference between city and highway driving in a traditional gasoline car, for example. In theory, if you drive less than 35 miles a day, you could drive the Volt forever and never (or practically never) have to put gas in it.

For our fuel economy calculations, we assume the Volt will be operated 70 percent on electricity and 30 percent on gasoline. However, as we have learned from owners in our forums, some drivers are saving even more fuel by operating almost exclusively on electricity:

• User carriegordo reports driving 7,000 miles on just 7.3 gallons of gas. That's less than a single tankful in the Volt's already small 9.3-gallon tank.

• User marclee reported that 2800 of the 3200 miles he's driven his Volt have been on electricity. That leaves just 400 on gas. (These numbers are easily retrieved from the efficiency screen on the Volt's central display.)

• User themajor1975 reported driving 11,000 miles on 62 gallons of gas.

• Two other forum users reported driving more than 2500 miles on 10.7 gallons of gas, and 500 miles on just one gallon.

All these users gave us enough information to calculate equivalent MPGe estimates based on their usage, assuming their cars get the same 32 mpg on gas and 2.93 miles per kWh on electricity as we measured in mixed driving. If the Volt buyers are anything like early Toyota Prius buyers, competing to get the best mileage may be a big deal. On that basis, carriegordo is in the lead, getting the equivalent of 93 mpg. Our newest Volt driver, with 500 miles on one gallon is close behind at 87 MPGe. Marclee, and the other anonymous driver are in a near dead heat for third place at 78 and 77 MPGe, respectively. And themajor1975 gets a still-respectable 72 MPGe.

All these make our 61 MPGe assumption, the best of any car we've tested save pure electrics, look almost puny.

Another user, burkham/krikorian, didn't tell us how far she's driven, but says she has owned her Volt for two months without filling the tank.

While these user experiences represent isolated examples, they effectively demonstrate the Volt's potential for saving fuel. If you frequently make long trips and rarely have the chance to charge, you may be better off buying a fuel-efficient Toyota Prius hybrid.

On the other hand, if you are one of the 78 percent of Americans the Volt was designed for, who normally drive less than 40 miles a day - and don't forget to plug in every night - the Volt can rack up tremendous fuel savings, even counting the electricity it uses. We've also found the Volt is really cheap to operate when it's running on electricity.

It also goes to show how variable the gas mileage of plug-in hybrids can be. Many inflated early references to mileage in the Volt made the nonsensical assumption that electricity is free. Remember GM's 230 mpg claim? The calculations effectively assumed the Volt used no electricity at all. Here at Consumer Reports, we don't count electricity as a freebie. But we will take our readers reports of their fuel usage at face value and applaud their commitment to saving gas.