Fuel efficiency is a feature most car buyers are concerned with, following months of gasoline prices drifting between $2 and $3 a gallon. Window stickers on new cars include a printout reporting the mileage figures from the Environmental Protection Agency (EPA). Trouble is, those figures are usually wrong — sometimes overstating actual mileage as much as 30 percent or more.

The problem is rooted in the EPA test, which dates back to the 1970s, and does not involve testing cars in today's real-life driving conditions. The existing 30-year-old tests appear to maximize mileage by keeping test vehicles' highway speeds below 60 mph, avoiding rapid acceleration, not factoring in idling time spent in traffic. The tests also fail to include using air conditioning and electronic features that can affect fuel economy.

The new test program will include more realistic conditions and, based on testing done by Consumer Reports magazine, the results will show significant drops in EPA mileage figures, especially for the highly touted gasoline-electric hybrid vehicles.

Overall, Consumer Reports reports that 90 percent of 303 cars and trucks it tested (including model years 2000 to 2006) failed to meet the EPA mileage figures.

The largest discrepancies were found with hybrid cars during city driving, where the actual miles-per-gallon was only slightly better than 50 percent of the EPA figure.

In the highway driving portions of the existing test, the hybrids, as well as most other cars, recorded miles-per-gallon figures only slightly lower than EPA estimates.

Still, the less dramatic fuel savings complicates the calculations for hybrid car buyers who must weigh the additional cost of the vehicle against the predicted fuel savings, which are now known to be lower than EPA estimates. This could lengthen the payback period by several years.

Many car buyers have long known that the EPA mileage figures were optimistic, but for the federal government to allow such highly overstated mileage estimates — and the associated under-stated costs of operation — to remain for so long is absurd. This is especially true with today's higher gasoline costs, which are not expected to decline due rapidly growing global demand from China and India and limited supplies.

Consumer Reports estimates that over five years of car ownership, some drivers will spend between $1,300 and $1,700 more for gasoline than the EPA sticker on their car predicted. As some reports on this topic have suggested, this is new version of sticker shock.

The new, more realistic EPA test — and the lower mileage figures — will begin appearing on the 2008 models. Until that time, prospective car and truck buyers should understand that the EPA figures are wrong, and do their research by checking Consumer Reports magazine to get an honest prediction of the real-world mileage figures.