Most say independence would make little difference (38 per cent) while a large number say it is too difficult to predict (32 per cent), a survey of 700 oil and gas firms by Aberdeen & Grampian Chamber of Commerce found.
But independence was the preferred option of those who expressed an opinion either way, with 18 per cent saying it would be positive against 12 per cent who said it would be negative.
Firms with fewer than 200 employees were most likely to say a vote in favour would be a positive development for the sector.
This uncertainty while Scotland decides is causing "more angst" than the outcome of the vote, according to law firm Bond Dickinson, which sponsored the survey.
A rising number of firms say the pre-referendum uncertainty is affecting their investment decisions, up from 38 per cent to 45 per cent in the last year.
This outcome is expected, according to Bond Dickinson partner Uisdean Vass.
Energy minister Fergus Ewing said: "It is very welcome that 56 per cent of oil and gas companies surveyed either believe that independence will be positive for the sector or will make little difference."
Better Together director Richard Baker, a Labour MSP, said: "It is clear that uncertainty over currency if we leave the UK is forcing oil firms to delay investment in Scotland."