PORTLAND  — One of the two rail lines over which oil is shipped through Maine is behind on reporting the volume of oil shipments to the Department of Environmental Protection.

DEP spokesman Jessamine Logan said Wednesday that Pan-Am Railways failed to report oil volume for April and May as required by law. The monthly reports must be submitted within 30 days.

The Portland Phoenix first reported on the overdue documents Wednesday.

Logan told The Associated press said the state grants leeway for vacations and illnesses that cause delays. But the April report is now more than a month overdue.

A spokeswoman for Massachusetts-based Pan-Am didn’t immediately return a call.

Logan says Pan-Am and Montreal, Maine and Atlantic Railway are the only rail companies that regularly ship oil through Maine.