Oil-rich nations have failed to reach an agreement on a production freeze at a lengthy summit in Qatar.Some media outlets reported that officials had indicated they needed more time to make the decision, as Iran did not attend the meeting and had vowed to keep pumping oil.It's also believed that the failed agreement on freezing production might lead to further drops in oil prices.Mohammed bin Saleh al-Sada, the Qatari Energy and Industry Minister, says the freeze could be more effective if major oil producers are included.However, he dodged questions about whether another special summit will be called before OPEC's next meeting, which is set to be held in June.So why is there such disagreement between major oil exporters?How much influence will the current stalemate have on big oil consumers like China and the US?And how sustainable are the current low oil prices?