By Patrick Bartlett BBC Europe business correspondent

Multinational oil giants BP and Shell have attempted to reassure the European parliament that they are taking steps to make their financial transactions more open and accountable.

At a special hearing on the embezzlement of oil revenues by corrupt third world governments, Shell vice-president Alan Detheridge said oil companies were often forced by governments to sign non-disclosure agreements.

But Mr Detheridge stressed that Shell was now declaring its payments made in Nigeria.

BP said that after tough negotiations, it was now doing the same in Angola.

Both companies added that they support a voluntary code of conduct on publishing oil industry payments being championed by British prime minister, Tony Blair.

But human rights groups believe that the code, even if agreed, is just a start.

Both they and the industry point out that more than half of many countries' oil revenues are channelled through state-owned oil companies.

Export agencies and other financial organisations who lend money to these companies would also need to be involved for the code to be effective.

Igo Herbert of the Nigerian-based Helping Hand group told the hearing billions of dollars of oil revenue was being embezzled by corrupt officials.

What was needed, he said, was a partnership between the oil companies and the international community to bring governments to account.

The International Monetary Fund (IMF) estimates that, in Angola alone, $1bn of oil revenue goes missing every year while three-quarters of the country's population lives in absolute poverty.