Japan’s purchase follows India’s Mangalore Refinery and Petrochemicals move to buy about 600,000 barrels of extra crude for July, two sources with direct knowledge of the matter said.

Saudi Arabia committed to meeting rising demand for crude in the second half of the year, aiming to lower prices which peaked at more than $127 a barrel for Brent in April.

The unilateral move came after the Organization of the Petroleum Exporting Countries failed to reach an agreement to increase output at a June 8 meeting.

Saudi Aramco had offered more crude to Asian refiners for July, but interest seems to have been lukewarm, a trading source said, adding that “just a handful” of refiners are expected to take “not big volumes” on top of that agreed in long-term contracts.

Five buyers in China, South Korea and Taiwan rejected the offer, trading sources said.

The first source indicated the additional volumes to Japan are limited, adding that very few buyers seemed to have the appetite for more oil next month, with spot trading for July already over.

Saudi Arabia did not specify the crude grades for the additional volumes, the source added.

Saudi Arabia’s oil output is expected to jump to nearly 10 million barrels per day in June from 8.86 million bpd the previous month, industry sources said, but it will pump slightly less in July.

US bank Goldman Sachs said in a report, meanwhile, that Libyan crude exports could hit 355,000 barrels a day in the short term from the rebel-controlled east, and that level is unlikely to prevent prices from heading higher in the second half of the year.

Exports from the North African producer could touch 585,000 bpd from additional shipments from fields in the west if there was a change in the government, the report said.

Libyan oil production fell from 1.58 million bpd in January to just 100,000 bpd in May, while exports have stopped entirely, according to the International Energy Agency.

“The opposition forces could resume about 200,000 bpd of crude exports as some fields and their related export terminals are largely intact. A further 155,000 bpd could potentially be exported at a later stage from a second loading port under their control,” Goldman Sachs said.

However, bringing back the remaining 1 million barrels of lost production will be challenging as some export terminals remain under government control, while several oil installations have also been severely damaged.

Supply disruptions in Libya and unrest in other oil producers in the region have put a premium of around $10-$20 a barrel to prices, traders and analysts have said.

Goldman Sachs said the recent slump in crude is temporary, and expects trading to remain volatile in the near-term before strong demand from China and India drives prices higher in the second half of 2011.

“We expect upward pressure on oil prices to increase in 2H11 as slower, but sustained, oil demand growth draws on inventory and OPEC spare capacity.”

Oil prices suffered their biggest weekly losses since early May last week on concerns over weaker economic outlook and the European debt crisis.