Iran has overhauled the way in which it offers contracts to foreign energy companies in a bid to attract up to $30 billion of new investment, BBC News reports.

The terms of the new oil contracts will be more favorable to foreign investors, who will be allowed a greater stake in long-term profits.

Iran is gearing up for the lifting of sanctions following the nuclear deal with six world powers in July.

The country has some of the biggest oil and gas reserves in the world.

The new contracts were announced at a conference in Tehran attended by many of the world's major energy companies, including BP, Shell, Total, Statoil and Sinopec. There were, however, no US companies present.

The energy majors are keen to exploit Iran's abundant reserves of oil.

The new contracts put an end to the so-called buyback model, which has historically deterred foreign investors, where overseas contractors developed and operated an oil field before handing it over to Iran.

Now, more lucrative longer-term contracts will be offered, where foreign companies can retain a stake in the field.

About 50 oil and gas projects were expected to be unveiled during the Tehran conference, taking place on Saturday and Sunday, November 28-29.

"The contract models introduced today are not perfect or ideal, but an effective and responsive model for both sides," Oil Minister Bijan Namdar Zanganeh said.