Royal Dutch Shell on Thursday said it plans to reduce its headcount by 6,500 this year owing to sliding oil prices and as it looks to complete a mega takeover.

"Today's oil price downturn could last for several years, and Shell's planning assumptions reflect today's market realities," the company said in a statement, adding that it anticipates "some 6,500 staff and direct contractor reductions in 2015".

Shell earlier this year unveiled a mega-takeover of British rival BG Group worth £47 billion ($73 billion, 67 billion euros), as the two firms consolidate their positions in a sector slammed by the oil price slump.

Also on Thursday, Britain's biggest domestic energy provider Centrica said it would reduce its workforce by a net 4,000 positions alongside a cost-cutting programme through to 2020.

Oil prices have plummeted by around half in value to around $50 a barrel since June last year because of the supply glut.

Shell on Thursday said "the company has to be resilient in today's oil price environment, even though we see the potential for a return to a $70-$90 oil price band in the medium term".