Until 1975, indirect taxes were the most profitable source of domestic revenue, especially such monopoly excises as the sales tax on salt. Other indirect taxes included those on alcohol, tobacco, sugar, radios, and livestock. Taxes ceased to exist with the abolition of currency during the Pol Pot regime and were replaced by payments in-kind. In 1984, the PRK introduced an agricultural tax to soak up profits earned by private farmers. The tax reportedly amounted to about 10% of total output. In 1986, taxes on private business were increased, which forced some shopkeepers out of business. In 2002, there was a general corporate tax of 9%, except for in the fields of resource exploitation.