Around 40 rig workers started a 24-hour strike on July 23 on the Alwyn, Elgin and Dunbar platforms in the British North Sea, curbing gas flows to shore, but stored crude was expected to mitigate any oil supply disruption.

The platforms halted production at 0500 GMT, said Unite, Britain's largest labor union. Unite and Total, which operates the platforms, earlier failed to agree on work shifts and pay, a union spokesman said.

No fresh talks are currently planned, another union spokesman said.

The fields account for about 10% of Britain's gas output, while their oil production contributes about 45,000 to 50,000 bbl/d 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 over half of the world's oil trades.

Brent futures were up 48 cents at $73.55 a bbl at 1321 GMT, off the day's high of $74.50.

Gas traders said the strike had curbed flows to shore, helping boost the within-day wholesale gas price by more than 2% to 58.50 pence per therm. The contract had already been at multi-year highs for this time of year.

The affected fields contribute around 10 percent of the Forties stream, but supply can be supported by using stored crude. July loadings of Forties were set at 330,000 bbl/d and August at 271,000 bbl/d.

A Total spokeswoman confirmed that industrial action had gone ahead "despite the new proposals that were made by the company".

Early this month, Unite announced that its members working at the Total platforms would stop overtime and go on a series of 12- and 24-hour strikes starting on July 23.

The other 24-hour stoppages are slated to take place on Aug. 6 and 20, while the 12-hour ones will occur on July 30 and Aug. 13.

Total is seeking to extend the time workers at its fields spend offshore to three-week rotations instead of two to match the rota system at its newly acquired Maersk fields.

"However, we're pleased to be able to continue discussions with staff at the Shetland Gas Plant and remain committed to further consultation and open dialogue with offshore staff," the spokeswoman said.

"What is at stake here is to ensure the long-term sustainability of our business in the North Sea, to enhance overall safety and remain the most efficient in our operations."

Other strikes are looming in the North Sea. Union workers at services company Aker Solutions announced their decision to strike at Equinor's non-producing Mariner platform, while 2,500 offshore oil service workers are being balloted for a possible separate strike.

Last week, 1,600 Norwegian rig drillers ended industrial action.

Offshore