In addition to our earnings release, we also issued a separate news release this morning regarding our agreement to purchase Everett Cash Mutual Insurance Company through a sponsored demutualization. We think this is reflective of our commitment to continue to pursue profitable growth of our specialty insurance business. Once the transaction closes, we expect ECM to be very well positioned from a capital and product perspective to pursue profitable growth geographically and through new product offerings. Now turning to the earnings release, our story of solid growth and profitability continued through the third quarter as we produced $248.2 million of consolidated pre-tax operating income.
On a per-share basis, comparable quarter-over-quarter results were $0.78 compared to $0.71, a 10% increase. Our average reinvestment rate on corporate bonds acquired during the quarter was 4.7% compared to the average yield rolling off of about 4.1%. We ended the quarter with book value per share of $26.19, which, inclusive of the regular dividend, equated to an increase of 18.5% year-to-date. That resulted primarily from our strong operating earnings and higher investment valuations.
Commercial auto, net premiums written grew 7% in the third quarter, while the loss ratio came in at 68.3 compared to 67.1 last year. Switching to workers' compensation, net premiums written grew 6.7% in the third quarter, while the loss ratio came in at 63.8 compared to 58.8 last year. Loss frequency trend continues to decline more than offsetting the increase in loss severity trend. We expect solid growth in profitability and specialty insurance to continue, reflecting the success of our specialty strategy and our growing contributions from our new specialty operating companies.