Japan dropped its corporate tax rate slightly on Sunday, to just more than 38 percent. That moved the United States to the top spot, with a 39.2 percent rate.

　　The U.S. has maintained that rate for two decades and it is unlikely to be changed in the coming months.

　　The United States is in the early stages of the political campaign leading to the national presidential election in November. The country's politicians have offered widely varying tax proposals, but have shown little inclination to reach agreement before the election.

　　Despite the official corporate tax rate, many U.S. businesses pay a sharply diminished proportion of their profits in taxes, sometimes nothing. They are able to legally reduce their taxes by deducting business expenses, and U.S. tax laws exempt some types of income from taxation.

　　One study, by the Organization for Economic Cooperation and Development [OECD], concluded American corporations paid an effective tax rate of about 24 percent. That was slightly less than the average for the 34-nation OECD coalition that promotes global economic advancement.

　　The OECD said that Ireland has the lowest tax rate among its members, a 12.5 percent rate. The island nation has used the rate to boost its economy, but other European nations have said it gives Ireland an unfair advantage in attracting corporations to locate there. Four other countries - the Czech Republic, the Slovak Republic, Hungary and Poland - have a 19 percent corporate tax rate.

　　U.S. President Barrack Obama, a Democrat, has called for corporate tax reform with a top rate of 28 percent.  he leading Republican seeking to oust him, one-time venture capitalist Mitt Romany, says he wants to cut the rate to 25 percent. Both say they want to overhaul the country's complex tax code, which would also affect the size of the tax bills that all American workers pay.