Seven people are potentially going for every job vacancy in Plymouth, research by the public sector union Unison has shown.
The city has the highest number of people out of work per job in Devon and Cornwall.
The findings come a day before publication of the Government's Strategic Defence Review.
The review is expected to herald cuts at Devonport naval base and dockyard, currently the city's biggest employer.
Plymouth is also regarded by some as vulnerable to the public sector cuts likely to be announced in the Comprehensive Spending Review, due to be published on Wednesday.
About a third of jobs in the city are in the public sector, according to independent research body Centre For Cities.
Ian Ducat, Unison's South West regional secretary, said: "Even now, before the major public spending cuts have hit home, there are more people unemployed than jobs to go around.
"Heavy job losses in the private and public sector will only lock the South West into a downward spiral.
"It will also cost the taxpayer billions in increased benefits and lost tax."
Unison's figures are based information from the Office for National Statistics on the number of Job Seekers' Allowance claimants per unfilled job centre vacancy in each of the region's council and unitary authority areas.
Torridge has an average of 5.4 people out of work per job, Torbay 4.3 and Cornwall and the Isles of Scilly 3.6.
Exeter has the lowest number of job seekers per job, 1.5, in the whole greater South West region.