Application to the Philippine setting of the world-wide correlation of CaO_6.0 and Na₂O_6.0 to crustal thickness agrees reasonably well with other methodology and earlier interpretations. Preliminary treatment of a growing geochemical database on Philippine volcanoes demonstrates that the thickness of the Philippine crust ranges from 15 to 65 km, with an average of about 30 km which is comparable to those of some neighboring island arcs namely Java, Halmahera-Sangihe, Ryukyu-Marianas, Vanuatu and Honshu. It appears that the Batanes crust as inferred from the geochemistry of the Iraya group of volcanoes is relatively thinner compared to those in the other parts of Luzon island.