Arouba, which beat Sohar 1-0 on Friday to take its points tally to 48 from 23 matches, has an unassailable lead of eight points ahead of second-placed Sur.
Sur, which needed to win on Saturday to keep its title hopes alive, faltered and settled for one point to take its tally to 40. It has two more games to play, but it can't catch up with its Sharqiyah rival, which has won the domestic title for the fourth time.
Arouba last won in 2008 and is placed fourth overall in the premier domestic league's honours list. Salalah giant Dhofar has won the top prize a record nine times, followed by Fanja (eight) and Al Nasr (five).
Al Nasr and Fanja are currently in third and fourth spots, respectively, with 38 points each and have three games left.
Arouba is likely to be awarded the OPL trophy during its home game against Sur at the Sur Sports Complex on May 16. Arouba is also in line for a domestic double as it takes on Sur for the His Majesty's Cup crown in Sur on May 22.
Other results: Fanja 2 Saham 1, Al Shabab 2 Musannah 1, Bausher 2 Al Nasr 2.