Hybrid cars aren’t living up to the hype, and it’s turning into a major disappointment for consumers, automakers and environmentalists.

There are two main problems. First, the system used to determine an automobile’s fuel economy by the U.S. Environmental Protection Agency judges performance based on “ideal” conditions. It’s not too cold, the air conditioner isn’t on, the driver doesn’t go faster than 60 miles per hour, acceleration is smooth and slow, and there’s no congestion. Nobody really drives like that, at least not all the time.

The second problem is that automakers have used hybrid technology to boost the power and performance of some vehicles, not to increase overall fuel efficiency. Hybrid technology, which supplements a combustion engine with an electric motor, does not automatically improve how many miles a gallon a car gets. In some models, it’s used to maintain fuel standards at current levels while bulking up the size of the vehicle or the power of the gasoline engine. Consumers get more muscle and break even on miles per gallon.

The Wall Street Journal reported Thursday that there has been a groundswell of complaints among hybrid owners that their new cars are not living up to expectations. Automakers told the paper they plan driving clinics to teach their customers about the technology and how to maximize fuel economy by changing driving habits. The EPA also says it will change the way it rates a vehicle’s mileage standards to more accurately reflect the way real people making real trips actually drive.

When consumers make the decision to spend more money to buy a hybrid vehicle, part of the calculation is the money they expect to save with increased fuel economy.

Until the EPA catches up to reality with its mileage math, buyers must beware. What the window sticker says and what the car will deliver aren’t necessarily the same thing.