What fuel octane does a 1975 El Camino use?

The 1975 Chevrolet El Camino's recommended octane rating depended on the engine. The owner's manual is the best source for this information. However, most engines from that year likely recommended regular unleaded fuel (87 octane), but some higher-performance engines might have called for mid-grade (89 octane) or even premium (91+ octane). You should not use leaded fuel in any 1975 vehicle.