General Motors said U.S. sales rose 12 percent in March to 231,052 units on strong demand for fuel-efficient cars and crossovers. The gain came primarily from Chevrolet, which reported a 17 percent increase in sales, to 173,073. GMC sales rose 12 percent to 34,337. Buick sales fell 16 percent to 13,105, and Cadillac sales dropped 13 percent to 10,537. It was the sixth straight month of decline for each brand. Through the first quarter, GM\'s overall sales gained 3 percent to 608,320 across the four brands. Retail sales, however, slid 1 percent in the first three months, GM said. The company\'s U.S. market share now stands at 17.5 percent, down from 19.4 percent a year earlier. Strong car sales With gasoline prices on the rise, March also was a strong month for GM\'s car sales, which climbed 22 percent from the March 2011 level. Sales of vehicles that achieve an EPA-estimated 30 mpg on the highway or better hit \"a record 100,000\" in March, the highest for any month, GM said in press release. \"The economy recovery and a deep bench of fuel-efficient cars and crossovers have been driving our sales for more than a year,\" Don Johnson, GM\'s vice president of U.S. sales, said. The subcompact Chevy Sonic has steadily increased sales since its launch in August 2011, with 8,251 sales last month. GM officials said about 60 percent of Sonic buyers are new to GM. Models with four-cylinder engines accounted for 42 percent of GM\'s U.S. sales mix last month, its highest ever, GM said. Record Volt sales Sales of the plug-in hybrid Chevrolet Volt also set a monthly record of 2,289 in March, a 50 percent increase over the previous high mark set in December 2011. About 7 percent of GM\'s Volt sales in March went to fleets. Sales of full-sized pickups rose 14 percent. GM is trying to build pickup inventories because it plans long factory shutdowns this summer for a model changeover. The March advance followed a 1 percent sales increase in February, which GM officials had said was better than expected given the big incentive-driven rise early last year. Johnson said GM\'s incentive spending for the first quarter was down about $400 per vehicle compared with the year-earlier period, though he did not give the exact amount of those incentives. He said fleet sales accounted for 26 percent of GM\'s total in March, compared with 25 percent in February.