Iraq opened on Wednesday, May 30 its fourth postwar bidding round for oil and natural gas exploration, with 39 foreign energy companies registered to compete for exploration rights in a dozen areas of the country, AP reported.

The government is seeking foreign investment to build up an energy sector hit by years of neglect and violence. Iraq holds the world's fourth largest oil reserves and oil revenues make up nearly 95 percent of the country's budget. Still, conditions for bidders are less attractive than in the three previous rounds held since the 2003 overthrow of Saddam Hussein.

Only areas with undetermined hydrocarbon resources are on offer, while previously the rights to known big and medium oil and gas fields were being auctioned off. Operating costs for energy companies could be high because most of the 12 exploration blocks are in remote and unsafe areas and lack infrastructure.

The government also added a clause for the first time that prevents companies from signing deals with regional authorities without the approval of the central government in Baghdad. Companies that violate the clause will have their contracts terminated, said Sabah al-Saidi, the deputy head of the Oil Ministry's Licensing and Petroleum Contracts department.

The new clause came in response to Exxon Mobil's bold move last year to sign six deals with Iraq's northern self-ruled Kurdish region without Baghdad's approval. In return, Baghdad banned the Texas-based company from taking part in the current bidding, but kept a deal to develop the 8.6-billion-barrel West Qurna Phase One oil field in the south.

Wednesday's auction started with no one bidding for an 8,000-square-kilometer (3,100-square-mile) block in northwestern Iraq with presumed natural gas fields.

Still, the current bidding round poses an opportunity for energy companies because the exploration blocks are in "fertile and easy-to-extract areas," said Kuwait-based independent analyst Kamel al-Harami.

The Iraqi Oil Ministry approved 47 international energy companies to participate in two days of bidding on Wednesday and Thursday, but only 39 companies paid the participation fee.

Top among the approved companies are the Anglo-Dutch Royal Dutch Shell, UK's BP, Chevron and Occidental of the U.S., China's CNOOC and CNPC, Japan's Japex, Russia's Lukoil and others.