(Reuters) – Exxon Mobil Corp’s first-quarter profit dropped less than expected in results posted on Thursday as margins at the refining unit of the world’s largest publicly traded oil company surged on tumbling crude prices. While pure exploration and production companies have been stung by low prices, integrated companies such as Exxon and Royal Dutch Shell are relying on their refining units to bolster their bottom lines. A 50 percent drop in crude prices since June has slashed the costs of feedstock for refiners. “It was a strong quarter (for Exxon),” said Brian Youngberg, analyst at Edward Jones in Saint Louis. “Their diversified model tends to hold up better in a weaker oil market and that is seen in this quarter.” Shares of Exxon rose 0.2 percent to $88.05 early Thursday afternoon. The Irving, Texas-based company earned a first-quarter profit of $4.9 billion, or $1.17 per share, down 46 […]