The FTSE 100 started the week on the backfoot, dragged lower by Shell and BP.
An hour into trade, London's blue-chip index is about six points down at 8,816, a loss of just under a tenth of a percent.
Apart from oil prices coming under pressure after OPEC agreed to increase production, Shell has also lowered its second-quarter guidance due to scheduled maintenance and the sale of its onshore oil and gas joint venture in Nigeria.
Commodities trader Gencore, retailer JD Sports and precious metals miners Fresnillo are also among this morning's losers.
At the other end, mining and energy engineer Weir Group, and Asia-focused lender Standard Chartered are top of the leaderboard.
Adding to the negative sentiment this morning is the pending expiry of the 90-day pause before new US tariffs are imposed on Wednesday. They'll come into effect on the first of August.
