The International Monetary Fund says oil exporting countries in the Middle East lost $390 billion in revenue due to lower oil prices last year, and should brace for losses of more than $500 billion this year.

The fund's economic outlook released Monday estimates that for 2016, oil exporting countries in the region will see revenues from these exports drop between $490 billion to $540 billion compared to 2014, when oil prices were higher.

IMF Director for Middle East and Central Asia Masood Ahmed says this translates into budget deficits and slower economic growth, particularly for countries like Saudi Arabia that are still heavily dependent on oil to finance their spending.

The IMF has encouraged reforms such as lifting subsidies and tightening public sector wage bills to offset the impact.