Stocks fell on Friday, spurred by a combination of trade tensions and mixed earnings reports from some of the world's biggest businesses. After starting the day in positive territory, the Dow Jones Industrial Average (DJINDICES: ^DJI) closed down 0.3%, and the S&P 500 (SNPINDEX: ^GSPC) ended the week with a steeper 0.7% decline.Data source: Yahoo! Finance.Oil stocks led the market lower, and the SPDR S&P Oil & Gas Exploration and Production ETF (NYSEMKT: XOP) fell 2%.