Oil prices trickled lower on Thursday as doubts the Opec oil cartel would be able to bring its quota busters under control overcame concerns about falling US oil supplies.
US light crude futures were trading at $33.80 a barrel, down 20 cents on the day but up almost four percent this week, largely propelled by Opec's surprise decision to cut production.
The Organisation of the Petroleum Exporting Countries, which controls half the world's oil export trade, pledged on Tuesday to cut its official supply limits by one million barrels per day to 23.5 million bpd from April 1.
The group also said it would immediately remove supply of 1.5 million bpd pumped by its members above self-imposed limits.
But Opec's biggest producer and exporter Saudi Arabia has told oil majors, most European customers and buyers in Asia that supplies in March would be unchanged from February.
"Opec's agreement had me concerned a bit about a bigger supply cut for March until I saw the notification this said an oil buyer in Japan, which is heavily reliant on Opec producers.
Abu Dhabi National Oil Co, the biggest producer in Opec-member United Arab Emirates, has also told Asian customers it would not make any cuts in March compared with February.
David Thurtell, commodities strategist at Commonwealth Bank of Australia in Sydney had indicated soon after Opec announced its decision from Algiers that quota discipline could prove a problem for the oil group.