How vulnerable are Latin American nations to international arbitration?
Venezuela makes the answer easy to find. The Bolivarian Republic owns $14.5 billion in direct investments abroad, mostly Citgo refineries and gas stations. It also enjoys $22.9 billion in accounts receivable, mostly for oil delivered by not paid for. Some of that are debts incurred by the Petrocaribe countries, but most of it is with the United States, and it is all potentially attachable in a settlement. (The liquid assets are probably owned by the central bank, which has $39 billion in reserves, and are considered immune.) Blocking those accounts receivable is the 21st-century equivalent of parking a gunboat in the harbor. Hugo needs to tread very carefully, and considering that Cemex is still being run from Monterrey, it looks like he has been.
How about Argentina? Mecon gives the answer for 2007 right here, on page 15. The Argentine government owns $8.2 billion in foreign assets. Sounds vulnerable! It's not, however. $6.0 billion consists of “créditos por financiación de entes binacionales.” The big one is the Yacyretá dam on the Paraguayan border, an $11 billion project. I suppose one can imagine a world in which ... uh ... no, I can't really imagine a world in which foreign investors in Argentina could go after Yacyretá. And given that it loses money, I'm not sure that they'd want to. Another $1.5 billion represents Argentina's paid-in capital to multilateral lending organizations like the IMF and World Bank. In theory, I suppose, that money is very vulnerable to an adverse ICSID (aka CIADI in Spanish) ruling, considering that ICSID is part of the World Bank group. In practice, I don't know of any cases where the a multilateral institution has reassigned capital from a national entity to a private interest. I don't even know how that would work, accounting-wise: the multilateral entity would need to find cash to pay the private investors for its shares, since only governments can hold capital stakes in multilaterals. That would get beyond messy right quick. In short, Argentina isn't all that vulnerable to the postmodern imperialism of the 21st century. So why not nationalize the airlines?
What about Ecuador? Sadly, its central bank does not make the figure easy to find. It does not track Ecuadorean foreign direct investment at all. And what it does track is not broken out into public v. private, save for central bank reserves. (Which is an odd concept in a dollarized economy, but the number is there.) I'm still stumped.