Robert- you can request a copy of your grandfathers birth certificate from Oran by sending a request to:

Monsieur la Presidente
De la APC de Oran ,
Oran Algérie

I received responses from Oran and Sidi-Bel Abbis. You can also write to the Bishop of Oran. The will research the parish recods of Oran for a small fee.
That address is:
EVECHE D'ORAN
2, RUE SAAD BEN REBBI 31007
ORAN EL-MAQQARI.

best of luck! Okey