PwC said 2015 may bring the first hostile takeover in the sector in living memory.
It warned of "uncertain times" for the estimated 440,000 people employed in the UK's oil and gas industry.
The oil price has fallen from $115 a barrel in the middle of the year to about $60.
Drew Stevenson, PwC's UK energy deals leader, said: "Oil prices remaining at the current level for a sustained period will light the touch-paper for mergers and acquisitions in 2015.
"As the UK industry positions itself for a more uncertain future, we expect to see deal activity levels pick up throughout the year ahead."
PwC said the industry would be "increasingly cash-constrained" with new debt coming at a cost, and existing debt coming under increased scrutiny.
