One in which the contract fixes a base price but contains a provision that in the event of specified cost increases, the seller or contractor may raise the price up to a fixed percentage of the base. (Spouses Concepcion vs. CA, G.R. No. 122079, 27 June 1997, citing Banco Filipino Savings and Mortgage Bank vs. Hen. Navarro and Del Valle, 152 SCRA 346)