(Reuters) -A slump in oil prices probably reduced Exxon Mobil's third-quarter upstream earnings by $600 million to $1 billion, the oil major signaled in a regulatory filing published on Thursday.

Oil prices fell by 17% in the third quarter, the largest quarterly decline in a year, on worries about the global oil demand outlook. Brent futures settled at $71.77 a barrel on the last trading day of the quarter.

The company, in its earnings snapshot, indicated weaker refining margins during the quarter would also hurt profits by up to $1 billion. Global fuel markets have been hit by softer consumer and industrial demand, especially in China where economic growth is slowing and electric vehicle use is on the rise.

Shares of Exxon closed at $122.58 each on Thursday. They were up just a 1 cent in after hours trading.

Exxon posted $7.07 billion in upstream earnings for the second quarter and a net profit of $9.1 billion in the year-ago third quarter, or $2.25 per share.

Analysts expect the industry giant to post an adjusted profit of $1.97 per share in the third quarter, according to estimates compiled by LSEG.