Toyota Motor Corp.’s Camry and Honda Motor Co.’s Civic, the top-selling mid-size and compact cars in the U.S., face risk of reduced production as inventory of the models rise, an RBC Capital Markets report said.

Toyota’s Camry exceeded its seasonal historical average inventory by more than 15 days supply in June and Honda carried about 25 days more Civics than usual, Joseph Spak, a New York-based analyst for RBC, said in today’s report. Camry and Civic were the only models identified as at risk for reduced output among 16 of the top-selling vehicles in the U.S. market.

General Motors Co., Ford Motor Co. and Chrysler Group LLC all added U.S. market share in the first six months of 2013, the first time that all three gained first-half share in 20 years. Models such as GM’s Chevrolet Cruze compact and Ford’s Fusion mid-size sedan, leading Detroit’s most competitive set of passenger cars in a generation, may need additional production to meet demand, according to RBC.

“Toyota is pulling out all stops to sustain its No. 1 market position against a slew of new competition,” wrote Spak, who has outperform ratings on both GM and Ford. “We continue to see downside risk to production schedules for the Civic line as inventories remain well above historical levels.”

Carly Schaffner, a spokeswoman for Toyota City, Japan-based Toyota, and Steve Kinkade, a spokesman for Tokyo-based Honda, didn’t immediately respond to e-mails asking for reaction to RBC’s report.

Growth by GM, Ford and Chrysler is driving industrywide sales to the highest since 2007, with analysts projecting 15.4 million cars and light trucks sold this year, according to the average of 18 estimates in a survey by Bloomberg News.

Cruze, Fusion

Sales of Detroit-based GM’s Chevy Cruze jumped 73 percent last month to 32,871, trailing only Toyota’s Camry at 35,870 among the top-selling passenger cars for June.

“Based on current production schedules and recent demand, it looks like the Chevy Cruze could use a little more stock,” Spak wrote.

Deliveries of Ford’s Fusion family car slipped 0.5 percent in June, which the Dearborn, Michigan-based company attributed to tight supply. Sales of the car climbed 18 percent in the first six months, and Ford is adding a second shift of 1,200 workers to its Mustang assembly plant in Flat Rock, Michigan, to start building Fusions there later this year.

“Fusion stock is improving, and will continue to improve as Flat Rock assembly gets up and running,” Spak wrote. “We see upside potential to production as Ford would like to get as many of these hot vehicles out.”

Market Share

Ford, the second-largest U.S. automaker, increased its market share by 0.8 percentage points in the first half to 16.5 percent, according to Automotive News Data Center. Market share for Auburn Hills, Michigan-based Chrysler, the third-biggest domestic carmaker, grew by more than 0.1 point to 11.6 percent. GM, the top-selling automaker in the U.S. market, boosted its share by less than 0.1 point to almost 18.2 percent.

Ford rose 1.1 percent to $16.88 at 10:15 a.m. New York time and GM increased 0.5 percent to $34.84. Ford climbed 29 percent this year through July 5 while GM surged 20 percent, both exceeding the 14 percent rise in the Standard & Poor’s 500 Index.