Declining oil revenue and a further cut in corporate income tax rates constrained revenue collection. For South-East Asia, total tax revenues as a share of GDP ranged between 12.4% in Indonesia and 19.6% in Thailand in 2013.20 While the “optimum” tax-to-GDP ratio would depend on a number of factors - such as a country’s preference for public goods, the availability of non-tax revenues and the structural characteristics of the economy - by all accounts, there seems to be room for increasing tax revenues in a number of countries. For instance, it was found in a study that Indonesia’s potential tax-to-GDP ratio is approximately 4-5 percentage points higher than the actual level (ESCAP, 2014a).