After riding high for more than five years, subcompacts are stalling in the U.S. market, with volumes fluctuating by plus or minus 1%-2% in each of the past six months.

The trend is notable because ever since the Japanese Big Three got back into the field in 2006, subcompact sales had been rising in line with higher gasoline prices, which continue to hover at $3.50-$4.00 a gallon nationally.

Illustrating the change is the 2.6% decline in Ward’s Lower Small segment last October. That month, the price of a gallon of regular unleaded nationally ranged $3.50-$3.75, per Energy Information Assn. data.

After dipping as low as $3.20 a gallon in the November-January period, a gallon of regular unleaded shot back up to $3.72 nationwide by late February.

But despite that rise in fuel costs, B-car sales fell from year-ago levels in both February and March, WardsAuto data shows.

The age of models typically plays a role in segment performance; the fresher the products the higher the demand.

Ward’s Large CUV segment, up 61.0% in the first quarter, benefits from the presence of a new Nissan Pathfinder and General Motors’ revamped Chevy Traverse, Buick Enclave and GMC Acadia trio.

But sales have atrophied in the Lower Small group, where most U.S. B-cars are found, even though the majority of models were redesigned within the past two years.

The segment’s 2.7% first-quarter volume decline can be blamed largely on the Hyundai Accent, down 24.7%; Mazda2, off 51.9%; and Toyota Yaris, down 27.9%; as well as slipping sales of the Chevy Sonic and Kia Rio, falling 8.0% and 8.3%, respectively.

All those models were new as of 2011 or 2012.

Improved first-quarter volume for the Nissan Versa and Ford Fiesta, up 11.6% and 3.3%, respectively, prevented the Lower Small sector from taking a steeper dive.

While the Versa sedan was all-new in 2011, the bigger-selling hatchback hasn’t been redesigned since 2006. A next-generation Versa 5-door is due this summer in the U.S.

Ford launched the Fiesta in the U.S. in 2011.

Industry insiders point to the narrow price and fuel-economy gaps that may be driving buyers away from subcompacts and toward larger compact models.

“I think for us, as well as with other car makers, the difference between compact and subcompact (models) in fuel economy isn’t so great, (and) the price-point delta really isn’t that great between the two,” Hyundai Motor America CEO John Krafcik tells WardsAuto in a recent interview.

“You just get so much more car when you get the compact,” he adds. “If you can buy an Elantra with all kinds of equipment for $18,500, why wouldn’t you buy that, instead of the subcompact with the similar price point?”

High Elantra residual values allow Hyundai to lease the car for as little as $159 a month in April, Krafcik says. That’s less than the lease cost of an Accent ($169), even though the Elantra’s sticker price is $1,000-$2,000 higher.

The ’13 Accent and Elantra sedan have identical combined fuel-economy ratings of 32 mpg (7.4 L/100 km).

Auto makers blame boxy styling that erodes aerodynamic efficiency and the weight penalty caused by added safety and comfort features for limiting subcompact fuel economy.

Sluggish subcompact demand isn’t preventing other auto makers from jumping into the fray, however. This year, Mitsubishi plans to launch its Mirage B-car in the market and Mercedes will add the A-Class to its U.S. lineup.

Further, with the U.S. government’s fleet fuel-economy target of 54.5 mpg (4.3 L/100 km) by 2025, the sector’s long-term outlook appears more positive.