Valero Energy Corp. reported a 49% fall in profit, hurt by weak margins and higher inventories. Refiners ramped up production in 2015, leading to higher inventories and weaker margins this year as demand softened during the mild winter.

Valero's refining throughput margin fell to $7.96 per barrel (bbl) in the first quarter of 2016, down from $12.39/bbl last year.

Net income attributable to shareholders fell to $495 million, or $1.05 per share, in the first quarter, which ended March 31. The 2015 first quarter saw $964 million, or $1.87 per share.

Operating revenue fell 26.3% to $15.71 billion in first-quarter 2016.

Up to May 2's close of $59.82, Valero's New York-listed shares have fallen 15.4% this year, while the Standard & Poor's 500 index oil and gas refining and marketing sub-index has fallen 13.3% over the same period.