BNSF Railway Co. reported a small year-over-year drop in coal revenue in the fourth quarter, which it attributed to low natural gas prices and mild weather.

The railroad's reported coal revenue was $965 million in the fourth quarter of 2017 — a 3% drop from the $996 million reported in the last quarter of 2016, according to an earnings press release, and down from the $1.01 billion reported in the third quarter.

Coal car volumes fell 9% year over year, while average revenue per car increased 6%. BNSF shipped 479,000 carloads of coal in the recent quarter compared to 524,000 cars a year ago.

Other factors responsible for the decline in coal revenue included high stockpiles at the facilities of BNSF customers and increased renewable generation.

Full-year totals were more positive, with a 14% increase in coal revenue compared to 2016.

BNSF's total revenue increased 6% from $5.31 billion in the fourth quarter of 2016 to $5.64 billion in the recent quarter. Full 2017 revenue increased 8%.