What makes you believe that somebody buying petro options with this contract will receive a discount of 40%?
Sorry 30% (not 40%), my mistake.
From the White Paper (page 21):
This first lot, which will be placed in the Pre-Sale, will have a volume of 3,400,000 Petro and will have a 30% discount on the reference price of crude oil in the Venezuelan basket. The following lots will have 5,000,000 Petro and the discount will decrease successively for each lot sold, until the last lot, of 24,000,000 Petro, which will have no discount.