GALVESTON, TX —American National Insurance Company (Nasdaq: ANAT) announced net income of $173.4 million or $6.44 per diluted share for the third quarter of 2018. Net income for the third quarter of 2018 increased by $105.7 million as compared to the third quarter of 2017 due to the inclusion of net unrealized gains on equity securities as required by new accounting guidance1 effective January 1, 2018. Excluding the impact of these net unrealized gains to provide a more consistent basis to compare these results to the prior period, net income for the third quarter of 2018 was $67.7 million or $2.52 per diluted share compared to net income of $73.3 million or $2.72 per diluted share for the third quarter of 2017. Net income for the third quarter of 2018 included $1.1 million of realized investment earnings compared to $31.0 million of realized investment earnings included in net income for the same period in 2017.
Net income for the nine months ended September 30, 2018 was $276.4 million. Excluding the impact of $115.1 million in net unrealized gains on equity securities reported in accordance with the new required accounting guidance (1) previously noted, net income for the first nine months of 2018 was $161.3 million compared to $149.1 million for the same period in 2017. Net income for the nine months ended September 30, 2018 included $20.7 million of realized investment earnings compared to $57.3 million of realized investment earnings included in net income for the same period in 2017.
Operating income for the third quarter of 2018 increased to $66.6 million or $2.48 per diluted share compared to $42.3 million or $1.57 per diluted share for the same period of 2017. Operating income increased due to better performance in our annuity and health segments and from additional investment income and reduced tax expense from certain actions including a significant contribution to our pension plan that improved the performance of our corporate and other segment.
For the nine months ended September 30, 2018, operating income was $140.6 million compared to $91.8 million for the same period in 2017. The increase in operating income for the first nine months of 2018 compared to the same period in 2017 is primarily attributable to improved performance in our corporate and other segment and our health segment.
Operating income excludes net unrealized gains (losses) on equity securities and realized investment earnings. Realized investment earnings are comprised of realized investment gains (losses), equity in earnings (losses) of unconsolidated affiliates and income (loss) from non-controlling interests.
Book value per diluted share as of September 30, 2018 was $199.55, compared to book value per share of $194.61 on December 31, 2017.
