It is but this is only the pre-sale (with discounts), which is a private sale reserved to institutional buyers. The public ICO will start on March 19th and will last until all coins will be sold.
I suspect this info might not be correct. AFAIK the "white paper" (better said, the "white papers" since there have been different revisions of it in the last few weeks) nowhere says that the pre-sale is
reserved to institutional buyers, it just says that it is private which is something completely different.
In fact if you register online on the official Petro site for the pre-sale you can register also as a "Persona natural", receive an e-mail for the offer, make an offer and receive a .pdf to finalize the pre-sale, while not being an "institutional buyer".
Moreover as per the declarations of Maduro and the government of Venezuela themselves there have been tens if not hundreds of thousands of "offers" (and users, both "companies" and "individuals") in the first days of the pre-sale, numbers and users categories which are incompatible with a sale supposedly
reserved to institutional buyers.
Yes, you can make an offer. But you cannot pay and get Petros yet (not even in the form of a contract), it is just a formal offer. I think that large institutional buyers might have been approached privately, but this is just my personal opinion. I doubt a Chinese or Indian oil refinery representative would register in the website as you and I, if they wanted to buy for example $20 million USD in Petros.
Anyway, before the ICO we cannot buy Petros. Also because the network is still under development.