Natural gas supplies in the United States grew last week, the government said Thursday. The Energy Departments Energy Information Administration said that natural gas in storage increased by 47 billion cubic feet to 3.308 trillion cubic feet for the week ended August 17. According to McGraw-Hills Platts, analysts had expected a rise of 36 billion to 40 billion cubic feet. The inventory level was 12.1 percent above the five-year average of 2.951 trillion cubic feet, and 14.7 percent above last years level of 2.885 trillion cubic feet, the government data showed.