Citigroup's Max Layton said oil prices will remain sharply volatile until there is clarity on a US-Iran deal, after Citigroup last month raised its Brent forecast by $15 to $110 per barrel. Traders said shipment delays hit a key crude loading terminal off Oman in April. Layton said the global physical crude market accumulated 700 million to 800 million barrels of buffer inventory over the past 12 months, but those stocks are being consumed quickly.