UPDATE 1-Thailand's PTT sees H2 net profit close to H1

* H2 revenue seen up from H1, oil rises to $70/bbl from $40

* Profit outlook depends on global economic uncertainty (Adds quotes, details)

BANGKOK Aug 18 (Reuters) - PTT PTT.BK, Thailand's biggest energy firm, said on Tuesday it expected second-half net profit to be close to the first half given its oil and gas businesses were under pressure from the weak economy.

But revenue for the second half would exceed that of the first as average oil prices rose to about $70 a barrel now from $40 early this year, Chief Executive Prasert Bunsumpun told reporters.

"In the second half, our profit should be close to the first half. Although oil prices have risen, the impact from the global economy is something unpredictable," Prasert said.

PTT, which runs the country's gas pipeline monopoly, posted a first-half net profit of 27.3 billion baht ($802 million), down 51 percent from a year earlier, on revenue of 690 billion baht, down 36 percent.

His comment was in line with market expectation. Kim Eng Securities expects PTT to report a 2009 net profit of 54.6 billion baht, which means second-half profit should be about the same as the first half.

PTT, which controls more than 30 petroleum, gas exploration, petrochemical and refinery businesses, should be affected by weak margins in the petrochemical business as new capacity from new plants due to come on stream later this year could drag down product prices, Prasert said.

At 0922 GMT, PTT shares were up 0.85 percent at 237 baht, while the overall market was 1 percent higher. ($1=34.02 Baht) (Reporting by Pisit Changplayngam; Writing by Khettiya Jittapong; Editing by Jason Szep)