The Detroit Three automakers posted double-digit gains in August US auto sales on Tuesday even as higher fuel prices drove a shift towards smaller and more fuel efficient vehicles. Sales growth by rival Toyota, however, outpaced them all. Toyota -- which saw sales collapse last year due to supply shortages in the wake of the devastating Japanese quake and tsunami -- said it gained 46 percent to 188,520 vehicles. Ford -- which posted a 13 percent gain with 197,249 vehicles sold -- estimated that total industry sales will rise to just above 1.3 million vehicles once all automakers report and to an annualized rate in the mid-to-high 14 million vehicle range. \"The economic fundamentals remain modest but stable,\" Ford economist Jenny Lin said in a conference call. \"This is still consistent for our outlook for the US economy to grow in the range of 2.0 to 2.5 percent this year.\" The second largest US automaker also announced plans to boost its fourth quarter production by seven percent to 725,000 vehicles and to add a third shift at its Louisville Assembly Plant to support demand for the new Escape small utility. \"As fuel prices rose again during August, we saw growing numbers of people gravitate toward our fuel-efficient vehicles -- cars, utilities and trucks,\" said Ken Czubay, Ford\'s head of sales. \"Customers increasingly value savings at the pump, and Ford is answering the call with a full family of vehicles with leading fuel efficiency and the power to choose which vehicle best meets their needs.\" GM posted a 10 percent gain in August sales to 240,520 vehicles. \"All four of our brands are building momentum behind new products so we\'re very well positioned as the economy continues to slowly improve,\" said Kurt McNeil, head of GM\'s US sales. GM said extensive national advertising during the Olympic Games helped boost Chevrolet passenger car sales -- which rose 25 percent in August with the Spark, Sonic, Cruze and Volt all posting their best-ever month. Fiat-controlled Chrysler posted a 14 percent gain to 148,472 vehicles as sales rose for all its models in \"the group\'s best August sales since 2007\". Fiat models led the sales pace, up 34 percent, and Chrysler sales rose 25 percent. \"Our hard work over the past few years is starting to pay some dividends in our sales growth, quality awards and profitability. Not to mention, an incredibly resilient U.S. new vehicle sales industry doesn\'t hurt either,\" said Reid Bigland, head of Chrysler group sales.