In the World Bank’s latest “Doing Business” report, an annual ranking of countries by the ease of doing business in each, Singapore retains the top spot as the country that is the easiest to do business in.

The tiny island nation has dominated this list for the past six years. It takes just three days to start a business in Singapore, according to the report, which is lower than the OECD average of five days and significantly lower than Asia’s average of nearly 30 days.

Apart from its business-friendly laws and flexible immigration policy, one big reason why Singapore has dominated the list for so long is its simple method for filing taxes. The report makes a case study of Singapore’s tax-filing system, which was converted to a simple, all-electronic process in 1992. From the report:

“Going electronic made administrative processes more efficient… The time needed to issue assessment dropped from 12-18 months to 3-5 months between 1992 and 2000… Automated standard taxation procedures also made the system less dependent on the subjective expertise of individual tax officers, reducing the potential for corruption.”

The U.S., which ranks No. 4 overall, is not even in the top 20 for its tax system. Ranking 64th on ease of paying taxes, the U.S. has a long way to go to catch up with Singapore.

Here are the World Bank’s top 20 most business-friendly nations: