HOUSTON, Oct 17 (Reuters) - Oil output in North Dakota,

the third-largest producing state in the U.S., is estimated to

have fallen by around 500,000 barrels through October, after

wildfires crossed into key producing counties earlier this

month, a state regulator said on Thursday.

Exxon Mobil ( XOM ) was among operators that last week

shut in some oil wells and production sites in the state in

response to the fires.

"My best estimate is around 500,000 total barrels

removed from those October numbers," said Justin Kringstad,

director of the North Dakota Pipeline Authority.

There were around 100,000 barrels per day (bpd) affected

in the immediate response to the fires, down to around 50-80,000

bpd in the week after, Kringstad added.

The state currently has 18 frac crews operating, down

from 20 last month, according to Mark Bohrer, assistant director

of the oil and gas division at the North Dakota Department of

Mineral Resources.

"We have 40 rigs running today even with the mergers and

acquisitions, our rig count has remained fairly steady," Bohrer

added.

Oil production in the state rose by 9,630 barrels per

day (bpd) in August, to an estimated 1.179 million bpd,

according to state regulators on Thursday.

And the number of producing wells in North Dakota in

August reached a record high, at 19,117 wells.

The state has also permitted three to four four-mile lateral

wells, which will help operators develop some of the tier two

and three locations that were previously economically more

challenging to drill, according to Bohrer.