Goldman Sachs lowered its outlook for crude prices. Fading business confidence in Germany, Europe's largest economy, also weighed on financial markets.
The Dow Jones industrial average fell 29 points, or 0.2 per cent, to 16,775 as of 12 p.m. Eastern Time Monday.
The Nasdaq declined 13 points, or 0.3 per cent, to 4,470. The Standard & Poor's 500 index slipped seven points, or 0.4 per cent, to 1,956. Energy stocks fell as oil languished around $80 a barrel in New York.
The energy sector was down 2.1 per cent, the biggest decline among the 10 S&P 500 sectors.