Saudi Arabia has switched its weekend to Friday-Saturday, bringing the kingdom into line with the other Arabian Gulf states.
The change from Thursday-Friday, which takes effect this weekend, will bring economic benefits, King Abdullah said.
It will "put an end to the negative effects and lost economic opportunities consistently associated with variation Ö between institutions and national bodies and international and regional counterparts", the king said.
The region's business community is expected to welcome the move, which brings the working week into step with elsewhere in the region.
"It's obviously very positive," said Rami Sidani, head of Schroder's Middle East & North Africa desk. "It'll minimise the lag.
"Before there was a long lag with international markets and the gap will be narrowed now."
The move may upset some traditionalists who have opposed such a change in the past on the ground that it would bring the kingdom closer to the Jewish and Christian traditions.
Even when the Shura Council, an advisory body to King Abdullah, decided in April to recommend changing the weekend, 41 of its 150 members voted against it.
Oman was the last of the six GCC states to push its weekend one day back to Friday-Saturday. The switch came into effect on May 1 after a decree by the ruler, Sultan Qaboos bin Said.
* Additional reporting by Hadeel Al Sayegh