LONDON (Reuters – The harsh Western sanctions and Russian rhetoric are raising doubts as to whether Russia’s government or its companies will pay their bonds, or default.

Last time Russia defaulted, it was 1998. The combination of large government spending, the Asian Financial Crisis and sharp drops in oil and other metals prices (Russia’s major revenue-earners) caused currency turmoil.

These are the four most important bond payments that you need to be aware of.

1) The bond due Tuesday at $417 mln is due to mature on Telecoms company VEON (NASDAQ;), formerly VimpelCOM. Although the shares of the company are listed in Amsterdam, a large portion of its operations is in Russia. Investors wonder if this might be the key to the mine. Shares plunged 27% Monday.

Russian Railways is due to pay a 23 Million Euro coupon on one its 2023 bonds. This payment will be made on March 6. This is another moment worth watching as the company is owned by the state.

Russian gas giant Gazprom, (MCX) has a $1.3 Billion bond that will be due to repay on March 7. This bond will serve as a major test for Moscow’s attitudes towards international capital markets.

It will continue to sell its gas to European clients and has more than $20 billion of cash left at the end last year. Vladimir Putin will not want the firm to pay. Are there any technical issues?

4) Russia will pay its next full bond payment on March 16, 2023. On March 31, 2030, a bond worth $359 Million will be due. Then on April 4, a $2 billion maturity will follow.

Morgan Stanley (NYSE:) It is estimated that due to various “grace periods” built into bonds, which give the borrower extra time for technical issues, the earliest sovereign default could be on April 15th. This is the date that 2023 bond coupons payments expire.