Oil prices dipped this morning as a relentless rise in US drilling undermined an OPEC-led push to tighten supply. 

Trading activity will be subdued today due to public holidays in China, the US and the UK. 

Brent crude futures were trading down six cents at $52.09 per barrel in early trade. 

US West Texas Intermediate (WTI) crude futures were down eight cents at $49.72 per barrel. 

The Organisation of the Petroleum Exporting Countries and some non-OPEC producers agreed last week to extend a pledge to cut production by around 1.8 million barrels per day (bpd) until the end of the first quarter of 2018. 

But the decision did not go as far as many investors had hoped and led to a heavy sell-off. 

An initial agreement, in place since January, would have expired in June this year. 

Despite the ongoing cuts, oil prices have not risen much beyond $50 per barrel. 

Much of OPEC's success will depend on output in the US, which is not participating in the cuts and where production has soared 10% since the middle of 2016 to over 9.3 million bpd, close to top producer levels Russia and Saudi Arabia. 

US drillers have now added rigs for 19 weeks in a row, to 722, the highest amount since April 2015 and the longest run of additions on record, according to energy services firm Baker Hughes. 

Almost all of the recent US output increases have been onshore, from so-called shale oil fields. 

Even if the rig count did not rise further, Goldman Sachs said it estimates that US oil production "would increase by 785,000 bpd between 4Q16 and 4Q17 across the Permian, Eagle Ford, Bakken and Niobrara shale plays." 

Analysts say that reducing bloated global fuel inventories will be key to reining in ongoing oversupply. 

While it is hard to come by reliable global oil inventory data, regional stock levels for the US, Europe and parts of Asia suggest that inventories have dipped in recent weeks, albeit from record levels.