As bruising year ends, U.S. refiners brace for more costly regulations

NEW YORK, Dec 16 (Reuters) - U.S. refiners such as Valero

Energy Corp and Marathon Petroleum Corp are

bracing for stricter, smog-busting gasoline regulations set to

hit in January, threatening more headwinds for an industry that

has just endured its least profitable year since the shale boom

started five years ago.

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