PORTLAND — UNUM Corp., the world’s leading disability insurer, reported Thursday a 15.4 percent increase in operating earnings per share over one year ago.

Operating earnings for second quarter 1997 increased by 9.6 percent over second quarter 1996. UNUM’s second quarter 1997 operating earnings were $83.2 million, or 60 cents per share, excluding after-tax realized investment losses of $1.7 million and a $6.1 million after-tax special item to recognize gains related to the previously announced sale of UNUM’s tax sheltered annuity (TSA) businesses.

UNUM’s second quarter operating results were driven primarily by higher earnings in the company’s group long term disability insurance line and its group life insurance business.

Operating income for second quarter 1996 was $75.9 million, or 52 cents per share, excluding after-tax realized investment losses of $2.0 million.

Second quarter 1997 net income was $87.6 million, or 63 cents per share, compared with net income of $73.9 million, or 50 cents per share, one year ago.