Peru has approved an environmental permit that will allow China National Petroleum Corp to do $1.39 billion of exploratory work in a natural gas block it is buying from Brazilian state-run oil company Petrobras. Block 58, in the southern Cusco region, which could hold several trillion cubic feet of natural gas, is now controlled by Petrobras. But CNPC said last year that it was taking control of the concession as part of its $2.6 billion purchase of all of Petrobras' Peruvian assets. CNPC, China's top oil and gas company, said Monday that the government could sign off on the transfer of block 58 by the end of May. "We expect the block to be transferred by May 30...but of course it's in the government's hands," said Claudia Bustamante, a spokeswoman for CNPC's local unit.