The countries with the largest budget deficits as of March 2015, in order, are Kuwait, Macau, the Republic of Congo, Norway, and Brunei. This is based on an examination of budget deficits as a percentage of gross domestic product (GDP), which puts all countries on a level playing field. Looking at it in terms of absolute budget deficit would lead to a much different outcome, but it would be skewed towards larger countries.
Even this list is somewhat skewed; it reflects the sudden weakness of oil in 2014, as it plunged more than 50% during the year. Many of these countries' budgets were made with assumptions of much higher oil prices. If oil prices were higher in previous or future years, this list would be composed of countries that are importers of oil.
Budget deficits are the amount that government spending exceeds revenues, typically computed on an annual basis. The government must issue bonds to make up the difference or dip into its savings. Interest rates on a country's bonds are determined by the market's evaluation of the country's ability to pay back its debt. Rising deficits lead to higher rates, especially if a country lacks sufficient savings.
Budget deficits, over time, eventually comprise a country's national debt. Each year's deficit or surplus determines the trajectory of the debt. Budget deficits are strongly correlated to the broader economy.
Increased economic activity leads to increases in tax revenues. Additionally, demand for government services declines as more people are employed. A strong economy boosts revenues and reduces expenditures. In contrast, a weak economy depresses tax revenues while increasing demand for government services.