With more electrified vehicles in the U.S. market than ever before, advanced-technology cars and trucks dominate best-in-class ratings in the government’s newly released Fuel Economy Guide for the ’13 model year.

Among the most popular classes of vehicles, Toyota’s Scion iQ EV boasts the best fuel economy of any car or light truck with a miles-per-gallon equivalent of 121.

But the mini-compact car, as it is classified by the federal government, suffers from limited availability. Toyota has scheduled just 90 units for U.S. distribution, most of which will arrive early next year and are targeted exclusively for car-sharing programs in urban centers and on college campuses.

The Japanese auto maker reversed plans earlier this year to sell the iQ at retail because its dealers, who sell more hybrid vehicles in the U.S. than any other franchise, reportedly were pessimistic about the car’s relatively steep price and limited range of 50 miles (80 km).

The Scion iQ EV is not alone in its dilemma. The handful of all-electric vehicles currently launching in the market by a number of auto makers are or will be available only in a limited number of markets.

Federal tax breaks of up to $7,500 still leave the cars priced thousands of dollars over sometimes identical models with fuel-efficient internal-combustion engines.

Sales of hybrids, plug-in hybrids and battery-powered EVs as a group remained a small but growing share of the market at 3.3% on volume of 428,545 units through November, compared with 2.1% in like-2011, according to WardsAuto data.

HEVs command the largest slice of the U.S. market with a 2.9% share, making up 89.7% of all advanced-technology vehicle sales with 384,511 deliveries.

The Toyota Prius is the most popular advanced-technology vehicle with deliveries of 184,037 units though November and a 42.9% share of the segment. The Camry Hybrid will end the year as a distant second, with 41,201 sales in the first 11 months, followed by the Prius C with 32,582.

The Chevrolet Volt is the fourth-best seller of the group this year and the highest-volume plug-in vehicle at 20,828 sales. The Chevy Malibu with eAssist stop/start mild-hybrid technology rounded out the top five with 15,283 deliveries through November.

Government’s figures show the Honda Fit EV ranks as the second most fuel-efficient vehicle behind the Scion iQ EV at 118 mpg-e and the most fuel-efficient small station wagon. The Fit EV, which began its rollout on the West Coast in July, sold 74 units through November, WardsAuto data shows.

The Smart Fortwo EV coupe and convertible are the third-most fuel-efficient vehicles on the government’s list and the best in the 2-seat segment, averaging 107 mpg-e. Daimler sold 139 Fortwo EVs in the U.S. in the first 11 months.

For the first time, the federal government also singles out the most fuel-efficient vehicles using conventional powertrains. Top models in combined-cycle testing include the 34-mpg (6.9 L/100 km) Audi A3 and Volkswagen Jetta small station wagons and 34-mpg Chevy Spark subcompact car.

Among fullsize pickup trucks, the Ram 1500 High Fuel Economy edition with 2-wheel-drive is cited for its segment-leading 21 mpg (11.2 L/100 km).

Hybrid versions of the Chevy Silverado 1500 and GMC Sierra 1500 in both 2- and 4-wheel-drive configurations also deliver 21 mpg in the government’s standard-pickup segment, although General Motors will discontinue those models next year. The auto maker sold 748 of the hybrid pickups through November.

The U.S. Environmental Protection Agency, which publishes the annual Fuel Economy Guide, later next year will release a second guide listing auto makers’ rankings for fleet fuel economy and vehicle emissions.