Refining margins dent Exxon, Chevron first-quarter results

HOUSTON (Reuters) - Weak refining margins dinged first-quarter results for Exxon Mobil Corp and Chevron Corp , though Chevron's oil production gains outshone its larger rival, which has struggled to turn operations around after recent missteps. Refining and chemical operations hurt two of the world's largest integrated energy companies for the second consecutive quarter, highlighting concerns about the impact of volatile oil prices on their businesses.