Of all the financial barometers highlighting the crisis in Venezuela, this may be the one that unnerves investors the most as oil sinks: The country’s foreign reserves only cover two years of bond payments.

The government and state-run oil company owe $21 billion on overseas bonds by the end of 2016, an amount equal to about 100 percent of reserves. Those figures explain why derivatives traders aren’t only betting that a default is almost certain but that it will most likely happen within a year.