FamilyMart Co Ltd and UNY Group Holdings Co Ltd said on Mar. 10 that they have agreed to merge in 2016, a move that would create Japan's second-biggest convenience store operator by sales.

Third-placed FamilyMart will be the surviving entity when it merges with the owner of fourth-ranked Circle K Sunkus in September next year, the companies said in a statement.

The pair said it will consider integrating the two convenience store chains under a single brand, though details including the merger ratio have yet to be decided.

FamilyMart and UNY on Mar. 6 said they were considering a merger to increase their competitiveness in a saturated market, grappling with a slump in consumer spending since a rise in the national sales tax last April.

Data from the Japan Franchise Association showed same-store sales at convenience stores fell 0.7 percent in January from the same period a year earlier, the 10th straight month of decline.

The merger would see the combined annual revenue of FamilyMart and UNY's convenience stores eclipse that of second-ranked Lawson Inc and close in on leader Seven-Eleven Japan, owned by Seven & i Holdings Co Ltd.

Shares of UNY have gained about 10 percent whereas those of FamilyMart have fallen 3.5 percent since the companies said they were studying a merger.

FamilyMart has a market value of about $4.3 billion, about three times UNY's $1.4 billion.