Employee works at Tawke oil fields in northern Iraq (file photo)The Iraqi government has opened bidding for development rights for some of the country's massive oil and gas fields.

More than 30 international firms, including U.S. giant Exxon Mobil and China's CNPC, are vying for a chance to secure service contracts to develop six oil and two gas fields.

The contracts will provide money to finance the country's reconstruction efforts.

The oil fields are estimated to hold about 43 billion barrels of crude.

Iraqi Oil Minister Hussain al-Shahristani says the goal is to increase oil production to 2.4 million barrels a day. He says producing at that level will provide the government with an extra $1.7 trillion over the next 20 years.

Some lawmakers have criticized the pending deals, saying that they are unconstitutional.

Oil companies awarded contracts will receive a fixed fee per barrel, over production targets, and not a share of the profits. They are also required to provide $2.6 billion in loans to Iraq to cover development costs.

Some information for this report was provided by AFP, AP and Reuters.