Oil was set for the biggest weekly drop in a month as market confidence in Opec’s ability to overpower a resurgent US shale industry wavered. US benchmark West Texas Intermediate fell below $50 a barrel on Friday — down $1.32 to $49.39 — by 6.45pm in London. The global Brent marker dropped $1.24 to $51.75 a barrel. Both benchmarks fell by more than 7 per cent this week, marking the biggest falls since early March. As supply curbs by Opec producers and those outside of the cartel took effect in January — sending prices higher in 2017 — US shale production has rebounded, locking the oil market into the middle of two competing forces. Data from US drilling company Baker Hughes on Friday showed that the number of rigs drilling for oil in the US rose for a 14th consecutive week. Drillers added five rigs in the week to April 21, bringing the total count to 688 — the most since April 2015. Analysts at Goldman Sachs said the price falls this week, however, were technical and not based on supply and demand fundamentals.