The North Sea is losing investment because of the windfall tax, political uncertainty and increased costs, according to a report.
Some 90% of offshore firms are cutting spending, equating to billions of pounds, said industry body Offshore Energies.
The organisation warned that a continued lack of investment would see production fall by 80% by 2030, which would increase the reliance on imports.
The Energy Profits Levy, which saw headline tax rates rise to 75% from 40%, combined with inflation, a lack of access to finance and an increase in material costs mean the sector is likely to produce 500mln fewer barrels of oil.
"By the mid-2030s, according to the Climate Change Committee, oil and gas will still provide half our energy needs,” said Ross Dornan from OEUK, cited by the BBC.
"We should be aiming to get as much as possible of that energy from our own resources - meaning the North Sea.
"That makes it essential for the UK to attract investment. The alternative is to become ever more reliant on other countries," Dornan added.