JX Holdings Inc. and TonenGeneral Sekiyu K.K., Japan's two biggest oil refiners, officially announced Thursday they intend to merge in April 2017, creating a company with control of more than half the country's gasoline market.

JX's wholly owned subsidiary JX Nippon Oil & Energy Corp. will merge with TonenGeneral, the No. 3 distributor by sales, around April 2017 through a share swap.

Oil titans JX and TonenGeneral will have combined sales of ¥14.3 trillion, compared with the ¥7.6 trillion of Idemitsu and Showa Shell combined.