At one time Toyota thought the Prius hybrid could be as big a seller as the Camry midsize sedan, which traditionally racks up more than 400,000 annual sales in the U.S.

In the near-term, the automaker thought it could increase U.S. sales of the car 30%.

But if this year’s performance of the new fourth-generation Prius sedan is any indication, neither of those predictions may come true.

The redesigned Prius sedan went on sale in January in the U.S. and in just one of the past six months did the 4-door post a sales increase compared with year-ago. In February, the car had a 1.4% increase adjusted for the daily selling rate, Toyota says.

From January through June, Prius sedan deliveries fell 10.5% from like-2015, with 48,475 units sold. That’s better than overall hybrid sales, which fell 15.5% through June.

However, WardsAuto data shows the extended year-over-year sales decline is unprecedented in the history of a new Prius sedan.

When the third-generation Prius debuted in June 2009, sales went up in 11 of the 12 ensuing months. A 3.0% DSR dip in October 2009 was the only downturn until June 2010’s 15.4% plunge.

The debut of the second-generation Prius in October 2003 began 28 straight months of year-over-year gains for the car, which finally experienced a 7.5% decline in February 2006.

What’s behind the fourth-gen Prius sedan’s lackluster performance? Opinions differ, but low fuel prices, a slew of new competitors in the green-car space, polarizing styling and America’s light-truck love affair all are factors, observers say.

“I think the majority of the issue with hybrid sales in general is obviously gas-related,” Paul Holdridge, vice president-sales for Toyota Div., Toyota Motor Sales U.S.A., says July 1 upon release of June 2016 sales results.

The national average for a gallon of regular unleaded was $2.28 on July 1, according to AAA. That compares with $1.59 ($2.08 adjusted for inflation) in 2003 and $2.35 ($2.63) in 2009.

Toyota has seen success this year with hybrid versions of its Highlander and RAV4 CUVs, as well as the Lexus RX hybrid CUV, playing to the notion the Prius’ body style may be limiting its market acceptance.

Analyst Dave Sullivan of AutoPacific cites as factors the popularity of light trucks due to low fuel prices, as well as some highly regarded new competition, such as the Chevy Malibu Hybrid.

A source close to Toyota, who wishes to not be named, concurs. While executives are putting a positive spin on the situation publicly, there is worry behind closed doors the new Prius is suffering from competition that may be more visually alluring or technologically advanced.

That includes plug-in hybrids such as the second-gen Chevrolet Volt, which can travel 53 miles (85 km) on battery power. The Prius has a smaller lithium-ion battery pack that assists, rather than substitutes for, gasoline power.