JKX Oil & Gas Plc (JKX) halted investment last week, citing a 55 percent tax imposed on gas production and a government decision to secure supplies for households by imposing restrictions on sales to industrial customers. The company joined Chevron Corp., Royal Dutch Shell Plc, Exxon Mobil Corp. (XOM) and Eni SpA, which quit Ukraine or froze projects in the past year. Others are set to follow, according to Bloomberg Industries.