Austrian oil and gas group OMV's Chief Executive Wolfgang Ruttenstorfer professed his innocence as his high-profile insider trading trial got under way on Thursday.

"I plead not guilty," he told a crowded courtroom in a clear voice after prosecutors laid out their case in a trial that has put Austria's reputation as a financial center in focus.

Ruttenstorfer has denied any wrongdoing in a share purchase he made in 2009, shortly before OMV announced a divestment that sent its stock higher, and has insisted the stock he got in a long-term option scheme did not lend itself to insider deals.

But Prosecutor Michael Schoen dismissed that reasoning.

"It doesn't matter if you were to keep the shares for two or three years if you bought them at a price which was less than they were actually worth," he told the Vienna court.

Looking relaxed and smiling, Ruttenstorfer shook hands with journalists and made jokes and small talk before taking the stand to confirm his personal details.

Ruttenstorfer, OMV chief executive since 2002, faces up to three years imprisonment if found guilty of insider trading. He could also face lesser charges or a fine. A verdict was due on Thursday.

He has said prosecutors were under pressure to use the case to prove their ability to secure a conviction for insider trading. The FMA financial watchdog has acknowledged the case was important for Austria's international reputation.

Austria has convicted only one person for the crime so far, handing out a suspended sentence, according to the FMA.

Mol Stake
Ruttenstorfer's contract as CEO expires in March and OMV stock has mostly not reacted to developments in the months-long case. Last August, the FMA asked state prosecutors to investigate 60-year-old Ruttenstorfer over the share deal that authorities say made him a 44,000 euro ($60,310) paper profit.

Ruttenstorfer bought €620,000 worth of OMV stock on March 23, 2009, more than doubling his holding to 40,030 shares. A week later OMV sold its 21% stake in Hungarian refiner MOL to Russia's Surgutneftegaz for €1.4 billion, in a deal priced at almost twice MOL's share price at the time.

The investigation also centered on an interview he gave to an Austrian magazine days before the divestment, in which he said OMV would hold on to the MOL stake that year.

He has been fined €20,000 in that case for market manipulation.

Ruttenstorfer, also on the board of Swiss drugmaker Roche , has worked for a total of 31 years at OMV, one of the largest energy companies operating in emerging Europe.

He served under former Social Democrat Chancellor Viktor Klima, who also started his career at OMV, from 1997-99.

OMV has a market capitalization of about €9.5 billion, making it Austria's second-largest listed company behind Erste Group Bank.