As yet, the anniversary celebrations have perhaps been more muted than usual on account of the virus, and there does not appear to have been any philatelic celebration of the anniversary, but whether there will be, remains to be seen. The exhibit here tells the story of the first 50 years of the organisation from its founding in Bagdad on September 14th, 1960.
The background to the formation of OPEC was that previously, the worlds oil supplies were largely controlled by activities of the 7 Sisters, that is the large international oil companies Chevron, Exxon, Mobil, Texaco, Gulf Oil, Anglo-Iranian Oil Company (now BP) and Royal Dutch Shell. These companies decided to reduce the posted price of oil without reference to the governments of the producing countries.
This lead to a very quiet meeting on the fringes of the 1st Arab Petroleum Conference, at the Maadi Yacht Club, in Cairo, in April 1959, between representatives of Iran, Iraq, Kuwait, Saudi Arabia and Venezuela which resulted in the Maadi Pact, a gentlemens agreement that was the precursor to the formation of OPEC, the following year.
If interested, you can see a short documentary film about 60 years of OPEC: by clicking here.
The OPEC website has a great deal of information about the organisation, and includes a special site for the 60th anniversary.