S&P Global Ratings estimates the large principal and interest repayments coming due over 2017-2020 of more than $20 billion, or about 21% of 2017 GDP.

"We expect that Ukraine will fulfill its short-term sovereign debt obligations in 2017 ($2.6 billion) and 2018 ($3.9 billion) given donor funds, existing foreign exchange and hryvnia balances held by The National Bank of Ukraine (NBU), and the government's ability to issue in both domestic and international markets," S&P said in its overview.

However, debt repayments in 2019 ($7.5 billion) – mostly the principal repayment of the sovereign eurobond and repayments to international financial institutions (including $1 billion to United States Agency for International Development) – remain dependent on the government's ability to pass the reforms required by the IMF and its ability to refinance some debt on the international market.

This year, S&P expects the Ukrainian government will issue a eurobond to test the market. "The effective interest rate on the entire outstanding stock of general government debt has increased with the increase in debt, although so has the weighted average maturity of Ukraine's debt stock," the overview said.

S&P experts say that large contingent liabilities, including two court cases relating to a $3 billion eurobond issued to Russia and a $31.8 billion litigation case filed by Gazprom against Naftogaz (for nonpayment in a potential take-or-pay contract), threaten the fiscal outlook (although Naftogaz has countersued Gazprom for a similarly large amount) and debt sustainability.

The Naftogaz arbitration ruling is due on June 30, 2017, while the conflict over the Russia-bought eurobond may drag on for longer.

"However, we understand that even an unfavorable ruling for Ukraine regarding the bond would not impair its ability to service its restructured and newly-issued bonds because a court-ordered freeze on these payments is not legally possible," they said.