Firstly, Chinese energy corporations often obtained property rights to oil fields or supply of oil or gas through investments in basic energy-related infrastructure. In most cases with Chad as an exception, China built oil refineries in countries with extensive oil fields or in countries where China imported crude oil. Sudan, Nigeria, and Algeria contained large oil fields, while Angola and Niger imported oil from China. Nigeria and Niger acted as examples of “construction work for oil and gas”. The CNPC purchased priority development rights in the OPL721, 732, 281, and 471 regions of Nigeria in May, 2006. Subsequently, the Chinese government promised to buy the Kaduna oil refinery in Nigeria, for US $2 billion. Furthermore, the CNPC’s construction work on oil refineries in Niger in November, 2008, propagated a three-year contract with the right of extraction in the Agedem region.