Renewable Energy Group Inc. announced Wednesday that it has expanded its line of credit agreement with Wells Fargo Capital Finance LLC from $40 million to $60 million. In a filing with the Securities and Exchange Commission, REG disclosed that two wholly owned subsidiaries exercised their option to expand the original line of credit, which was obtained in 2011. In addition to the line increase, the modification also increases the Ames-based biofuels and chemicals producer’s ability to issue letters of credit from $10 million to $25 million. “As our business continues to grow, so does our need for additional working capital,” said Chad Stone, REG’s chief financial officer. “We built this option into the original agreement in anticipation of future needs.”