NEW YORK (AFP) - US oil giant ExxonMobil reported an 18 per cent decline in quarterly profits on Thursday due to weaker refining earnings, but results bested expectations as oil and gas output stabilised.

Exxon, the largest US oil company, said third-quarter profits were US$7.9 billion (S$9.78 billion) on revenues of US$112.4 billion, down from US$9.6 billion on revenues of US$115.1 billion in the year-ago period.

Those results translated into earnings per share of US$1.79, two cents above analyst estimates. Revenues bested expectations by about US$5 billion.

Like other oil majors, such as Anglo-Dutch heavyweight Royal Dutch Shell, ExxonMobil was hit by weaker profit margins in the refining business.

Results for the segment nosedived to US$592 million from US$3.2 billion in the year-ago quarter.

However, ExxonMobil's oil and gas output registered a 1.5 per cent increase thanks in part to project ramp-ups in Canada and Nigeria.

ExxonMobil has seen declines in production in recent quarters, dipping 1.9 per cent in the second quarter and 3.5 per cent in the prior quarter.

Results in the upstream division, which comprises exploration and production activities, rose US$740 million to US$6.7 billion.

"ExxonMobil's third quarter results reflect our continued progress across a diverse set of profitable growth opportunities, which positions us well to deliver shareholder value," said chief executive Rex Tillerson.

ExxonMobil shares were up 0.8 per cent in pre-market trading.