Investors were keeping careful watch on President Barack Obama's drive to win support in Congress for a military strike on Syria.
The Dow Jones industrial average rose 108 points, or 0.7 per cent, to 14,942 in shortly before noon Wednesday.
The Standard & Poor's 500 index rose 14 points, or 0.9 per cent, to 1,654 and the Nasdaq composite was up 36 points, or 1 per cent, to 3,648.
U.S. automakers rose sharply. General Motors gained $1.05, or 3.1 per cent, to $35.20 and Ford rose 52 cents to $16.87.
GM's sales rose 15 per cent last month, while Ford's rose 12 per cent.