Around 40 union members started strike action last Monday, stopping work for 24 hours at the Alwyn, Elgin and Dunbar platforms in the North Sea, but stored crude cushioned against any immediate oil supply disruption.
Unite the Union, Britain's largest labour union, has scheduled further 24-hour stoppages on August 6 and 20 and a 12-hour strike on August 13 if it is unable to reach agreement about new rotas with Total.
The fields account for about 10 per cent of Britain's gas output, while their oil production contributes about 45,000 to 50,000 barrels per day (bpd) to the Forties and Brent Blend crude streams.
Forties and Brent Blend are key oil grades used to set the dated Brent benchmark that prices more than half of the world's oil trades.
A strike at Total's Shetland gas plant planned for Monday has been suspended to allow discussions to continue, the spokesman said.
Unite is also preparing to ballot 2,500 offshore oil service workers for another possible strike over pay, which would affect 106 North Sea oil platforms.