PTT, Thailand's top energy firm, reported a 0.4% fall in quarterly net profit on Friday, held down as expected by foreign exchange losses, lower gas sales volume and weaker profits from its refinery and petrochemical businesses.

Earnings at PTT, Asia-Pacific's third-biggest listed oil and gas firm by market value, are expected to improve in the fourth quarter as a recovery in gas demand and higher oil prices should help offset the impact of floods in Thailand, analysts said.

"PTT had good earnings in the first and second quarters. This quarter should be the lowest and we expect a pick-up in the fourth quarter," said Parin Kitchatornpitak, senior analyst at KTB (Thailand) Securities.

"Global oil prices are rising in line with higher demand. This should bode well for PTT's normal operations. Its refinery and petrochemical subsidiaries should improve in the fourth quarter," Parin added.

Global benchmark Brent crude traded above $123 a barrel on Friday, back near the recent high of around $126 in April.

Thailand's largest listed company by market value posted a July-September net profit of 21.6 billion baht ($703 million), or 7.57 baht per share, down marginally from 21.7 billion baht a year earlier.

Nine analysts polled by Reuters had on average estimated net profit would be 21 billion baht.

PTT earnings were weaker than those of regional peers, which reported a rise in quarterly net profit as strong oil and gas production growth offset refining losses.

China's No.1 and No.2 oil and gas producers, PetroChina and China Petroleum & Chemical Corp (Sinopec) , reported third-quarter net profits that beat estimates.

The company is expected to post a 26% rise in 2011 net profit to 105 billion baht, according to Thomson Reuters I/B/E/S. It posted nine-month net profit of 88.65 billion baht ($2.9 billion), up 44% from a year earlier.

PTT, valued at $27 billion, runs Thailand's gas pipeline monopoly and controls more than 30 petroleum, gas exploration, petrochemical and refinery businesses.

It ranks behind PetroChina and Sinopec in market value among oil and gas companies in Asia.

Third-quarter revenue rose 40% on the year to 648 billion baht, but revenue from its exploration, petrochemical and coal businesses dropped from the second quarter , it said in a statement.

It had a foreign exchange loss of 5.23 billion baht but booked a profit from petrochemical and refinery units of 4.47 billion baht, up from 3.28 billion a year earlier.

PTT shares fell 22% in the third quarter, underperforming a 12% fall in the broader market.